WASHINGTON - The U.S. military quietly waged a campaign from Ethiopia last month to capture or kill top leaders of al-Qaida in the Horn of Africa, including the use of an airstrip in eastern Ethiopia to mount airstrikes against Islamic militants in neighboring Somalia, according to U.S. officials.

The close and largely clandestine relationship with Ethiopia also included significant sharing of intelligence on the Islamic militants' positions and information from U.S. spy satellites with the Ethiopian military. Members of a secret U.S. Special Operations unit, Task Force 88, were deployed in Ethiopia and Kenya, and ventured into Somalia, the officials said.

The counterterrorism effort was described by U.S. officials as a qualified success that disrupted terrorist networks in the East African nation, led to the death and capture of several Islamic militants and involved a collaborative relationship with Ethiopia that had been developing for years.

But the tally of the dead and captured does not as yet include some Qaida leaders - including Fazul Abdullah Mohammed and Fahid Mohammed Ally Msalam - whom the United States has hunted for their suspected roles in the attacks on U.S. embassies in Kenya and Tanzania in 1998. With Somalia still in a chaotic state, and U.S. and African officials struggling to cobble together a peacekeeping force for the war-ravaged country, the long-term effects of recent U.S. operations remain unclear.

It has been known for several weeks that U.S. Special Operations troops have operated inside Somalia and that the United States carried out two strikes on Qaida suspects using AC-130 gunships. But the extent of U.S. cooperation with the recent Ethiopian invasion into Somalia and the fact that the Pentagon secretly used an airstrip in Ethiopia to carry out attacks have not been previously reported.

The secret campaign in the Horn of Africa is an example of a more aggressive approach the Pentagon has taken in recent years to dispatch Special Operations troops globally to hunt high-level terrorism suspects. President Bush gave the Pentagon powers after the Sept. 11 attacks to carry out these missions, which historically had been reserved for intelligence operatives.

When Ethiopian troops first began a large-scale military offensive in Somalia late last year, officials in Washington denied that the Bush administration had given its tacit approval to the Ethiopian government. In interviews over the past several weeks, however, officials from several U.S. agencies with a hand in Somalia policy have described a close alliance between Washington and the Ethiopian government that was developed with a common purpose: rooting out Islamic radicalism inside Somalia.

The Pentagon for several years has been training Ethiopian troops for counterterrorism operations in camps near the Somalia border, including Ethiopian special forces called the Agazi Commandos, which were part of the Ethiopian offensive in Somalia.

Bryan Whitman, a Pentagon spokesman, declined to discuss details of the U.S. operation, but some officials agreed to provide specifics because they saw it as a relative success story. They said that the close relationship has included the sharing of battlefield intelligence on the Islamists' positions - the result of an Ethiopian request to Gen. John P. Abizaid, then the head of the U.S. Central Command. John D. Negroponte, the director of national intelligence at the time, then authorized spy satellites to be diverted to provide information for Ethiopian troops, the officials said.

The deepening U.S. alliance with Ethiopia is the latest twist in the United States' on-and-off intervention in Somalia in the past two decades, beginning with an effort to distribute food to starving Somalis and evolving into deadly confrontation in 1993 between U.S. troops and fighters loyal to a Somali warlord, Mohamed Farrah Aidid. The latest chapter began last June when the Council of Islamic Courts, an armed fundamentalist movement, defeated a coalition of warlords backed by the CIA and took power in Mogadishu, the capital. The Islamists were believed to be sheltering Qaida militants involved in the embassy bombings, as well as in a 2002 hotel bombing in Kenya.

After a failed CIA effort to arm and finance Somali warlords, the Bush administration decided on a policy to bolster Somalia's weak transitional government. This decision brought U.S. policy in line with Ethiopia's.

As the Islamists' grip on power grew stronger, their militias began to encircle Baidoa, where the transitional government was operating in virtual exile. Ethiopian officials pledged that if the Islamists attacked Baidoa, they would respond with a full-scale assault.

While Washington resisted officially endorsing an Ethiopian invasion, U.S.