Three months after the United States successfully pressed the United Nations to impose strict sanctions on North Korea because of the country’s nuclear test, Bush administration officials allowed Ethiopia to complete a secret arms purchase from the North, in what appears to be a violation of the restrictions, according to senior American officials.

The United States allowed the arms delivery to go through in January in part because Ethiopia was in the midst of a military offensive against Islamic militias inside Somalia, a campaign that aided the American policy of combating religious extremists in the Horn of Africa.

American officials said that they were still encouraging Ethiopia to wean itself from its longstanding reliance on North Korea for cheap Soviet-era military equipment to supply its armed forces and that Ethiopian officials appeared receptive. But the arms deal is an example of the compromises that result from the clash of two foreign policy absolutes: the Bush administration’s commitment to fighting Islamic radicalism and its effort to starve the North Korean government of money it could use to build up its nuclear weapons program.

Since the Sept. 11 attacks, as the administration has made counterterrorism its top foreign policy concern, the White House has sometimes shown a willingness to tolerate misconduct by allies that it might otherwise criticize, like human rights violations in Central Asia and antidemocratic crackdowns in a number of Arab nations.

It is also not the first time that the Bush administration has made an exception for allies in their dealings with North Korea. In 2002, Spain intercepted a ship carrying Scud missiles from North Korea to Yemen. At the time, Yemen was working with the United States to hunt members of Al Qaeda operating within its borders, and after its government protested, the United States asked that the freighter be released. Yemen said at the time that it was the last shipment from an earlier missile purchase and would not be repeated.

American officials from a number of agencies described details of the Ethiopian episode on the condition of anonymity because they were discussing internal Bush administration deliberations.

Several officials said they first learned that Ethiopia planned to receive a delivery of military cargo from North Korea when the country’s government alerted the American Embassy in Addis Ababa, Ethiopia’s capital, after the adoption on Oct. 14 of the United Nations Security Council measure imposing sanctions.

“The Ethiopians came back to us and said, ‘Look, we know we need to transition to different customers, but we just can’t do that overnight,’ ” said one American official, who added that the issue had been handled properly. “They pledged to work with us at the most senior levels.”

American intelligence agencies reported in late January that an Ethiopian cargo ship that was probably carrying tank parts and other military equipment had left a North Korean port.

The value of the shipment is unclear, but Ethiopia purchased $20 million worth of arms from North Korea in 2001, according to American estimates, a pattern that officials said had continued. The United States gives Ethiopia millions of dollars of foreign aid and some nonlethal military equipment.

After a brief debate in Washington, the decision was made not to block the arms deal and to press Ethiopia not to make future purchases.

John R. Bolton, who helped to push the resolution imposing sanctions on North Korea through the Security Council in October, before stepping down as United Nations ambassador, said that the Ethiopians had long known that Washington was concerned about their arms purchases from North Korea and that the Bush administration should not have tolerated the January shipment.

“To make it clear to everyone how strongly we feel on this issue we should have gone to the Ethiopians and said they should send it back,” said Mr. Bolton, who added that he had been unaware of the deal before being contacted for this article. “I know they have been helpful in Somalia, but there is a nuclear weapons program in North Korea that is unhelpful for everybody worldwide.

“Never underestimate the strength of ‘clientitis’ at the State Department,” said Mr. Bolton, using Washington jargon for a situation in which State Department officials are deemed to be overly sympathetic to the countries they conduct diplomacy with.

Sean McCormack, the State Department spokesman, declined to comment on the specifics of the arms shipment but said the United States was “deeply committed to upholding and enforcing U.N. Security Council resolutions.” Repeated efforts to contact the Ethiopian Embassy were unsuccessful.

In other cases, the United States has been strict in enforcing the Security Council resolution. For instance, late last year, American intelligence agencies tracked a North Korean freighter suspected of carrying illicit weapons and pressed several nations to refuse to allow the ship to dock. Myanmar, formerly Burma, allowed it to anchor and insisted that there was no violation.

North Korea conducted its first nuclear test on Oct. 9, and the Security Council resolution, adopted less than a week later, was hailed by President Bush as “swift and tough,” and a “clear message to the leader of North Korea regarding his weapons programs.”

Among the biggest sticking points during the negotiations over the resolution were Chinese and Russian objections to language requiring inspections of ships leaving North Korea. The United States repeatedly pressed China and Russia to agree to the inspections, saying they were essential to enforcing the resolution’s embargo on North Korea’s sale of dangerous weapons, like ballistic missiles. In addition to the ban on the purchase of weapons from North Korea, the resolution also called for a ban on the sale of luxury goods to it and the freezing of its financial assets in banks worldwide.

The measure had special relevance for several African states that have long purchased low-cost military equipment from North Korea. Ethiopia has an arsenal of T-55 tanks that it acquired years ago from the Soviet Union and Eastern European nations. For years, it has turned to North Korea for tank parts and other equipment to keep its military running.

The Ethiopians bought the equipment at a bargain price; the North Koreans received some badly needed cash. In 2005, the Bush administration told Ethiopia and other African nations that it wanted them to phase out their purchases from North Korea. But the Security Council resolution put an international imprimatur on the earlier American request, and the administration sought to reinforce the message.

“They really are one of the larger conventional arms purchasers from North Korea, and we’re pressing them hard and saying, ‘Let’s get you out of that business,’ ” said the American official.

Another American official, who is involved in Africa policy, said: “These are cash on the barrel transactions. The Ethiopians know that they can get the best deal in Pyongyang,” a reference to North Korea’s capital.

In late January, the Central Intelligence Agency reported that an Ethiopian-flagged vessel had left a North Korean port and that its cargo probably included “tank parts,” among other military equipment.

American officials said that the ship, the Tekeze, a modern vessel bought from a company in Montenegro and named after an Ethiopian river, unloaded its cargo in Djibouti, a former French colony where the United States has based Special Operations troops and other military forces. From there, the cargo was transported overland to Ethiopia.

The Security Council resolution’s list of prohibited items included spare parts. Because the cargo was never inspected, some administration officials say the United States cannot say for certain that the shipment violated the resolution.

It is not clear if the United States ever reported the arms shipment to the Security Council. But because the intelligence reports indicated that the cargo was likely to have included tank parts, some Pentagon officials described the shipment as an unambiguous Security Council violation.

American officials said the Ethiopians acknowledged that the ship was en route and said that they needed the equipment to sustain their Soviet-era military. Ethiopia has a longstanding border dispute with Eritrea, but of more concern to Washington, Ethiopia was also focused on neighboring Somalia, where Islamic forces that had taken over Mogadishu, Somalia’s capital, six months earlier and were attacking Baidoa, the seat of a relatively powerless transitional government that was formed with the support of the United Nations.

The timing of the shipment was extremely awkward, as the Ethiopian military was preoccupied with Somalia and also quietly cooperating with the United States. Ethiopia began an offensive in Somalia to drive back the Islamic forces and install the transitional government in Mogadishu late last year. The United States was providing it with detailed intelligence about the locations of the Islamic forces and was positioning Navy ships off Somalia’s coast to capture fighters trying to escape the battlefield by sea.

On Jan. 7, American AC-130 gunships launched two strikes on terrorist targets from an airstrip inside Ethiopia, though it did not appear that the casualties included any of the few top operatives of Al Qaeda American officials suspected were hiding in Somalia.

After some internal debate, the Bush administration decided not to make an issue of the cargo ship.

American officials insist that they are keeping up the pressure on Ethiopia. While Ethiopia has not provided an ironclad assurance that it will accept no more arms shipments from North Korea, it has told the United States that it will look for other weapons suppliers.

“There was a lot going on at that particular moment in time,” said the senior American official. “They seem to have the readiness to do the right thing.”