NAIROBI, JULY 8 -- President Daniel arap Moi's crackdown on political opponents and human rights advocates has aggravated already tense relations between the United States and Kenya, prompting a congressional review that could freeze or cut economic and military aid to this East African country.

Kenya, which had long been recognized by the West as a beacon of political and economic stability in a region otherwise noted for chaos and conflict, is the largest recipient of American aid in sub-Saharan Africa, receiving $49.8 million in economic and military assistance this year and tentatively set to get about the same amount next year.

However, the government's crackdown against proponents of greater democracy here -- which has seen at least 11 dissidents detained in the last week and dozens of civilians injured during riots -- has triggered strong protest from the U.S. and other Western governments which, together with multilateral donors, contribute more than $940 million annually in aid to Kenya's economy.

In a development that could further strain U.S.-Kenyan relations, U.S. Ambassador Smith Hempstone said late tonight that human rights lawyer Gibson Kamau Kuria, who was once detained for nine months by Moi's government, had fled to the U.S. Embassy on Saturday morning and been granted refuge.

Hempstone said Kuria, who won the 1988 human rights award presented by the Robert F. Kennedy Memorial Center, has "indicated that he would like to leave the country," and the ambassador added that the U.S. government would try to facilitate that request.

On Friday, the State Department issued a statement expressing "distress" over the arrests of the dissidents and again urged the Moi government to respect individual rights of freedom of expression and assembly, which have eroded in recent years.

That request came two weeks after top congressional leaders sent a letter to Moi expressing concern for human rights in Kenya. The leaders did not receive a reply.

After the crackdown continued last week with the arrests of two opposition politicians, Kenya's ambassador to the United States, Denis Afande, was told by an American official that Congress would interpret the clampdown as Moi's official response to the letter, congressional sources said.

"The Hill's response to Moi will be to look again at assistance to Kenya," said a congressional source. "We are developing a strategy to cut aid."

The source said such a strategy could entail freezing funds already allocated for Kenya this year or cutting back funds appropriated for 1991. Congress, currently in recess, will resume its session Tuesday.

For some time, U.S. officials in Washington and Nairobi have been trying to encourage the Moi government to allow a public debate on multi-party democracy in this one-party state, and to consider moves to bring about such a political system.

At a time when democratic values and political pluralism are winning favor in other parts of Africa and the world, the 12-year Moi regime has clung to centralized control and rigid one-party rule, expressing fears of tribal factionalism if more than one political party is allowed to compete for power.

In recent years, particularly after an attempted military coup in 1982, all manner of dissent has been stifled in Kenya, including the banning of numerous publications accused by the rulers of subversion.

During a visit to Washington in February, Moi was told by American officials that U.S. assistance to Kenya would be tied more closely to political accountability and economic freedom here. Moi, whose government has been plagued by charges of widespread official corruption, visited the United States at a time when this nation is steadily losing foreign investment and forecasting a nearly $1 billion trade deficit for next year.

For a while after his trip to Washington, Moi appeared to consent to a public debate of the merits of multi-party politics. But the Kenyan leader never wavered from his opposition to allowing more parties, and accused supporters of political pluralism of being subversives and suffering from "insects in their heads."

Then, Moi declared the debate over last month when two former members of Moi's cabinet, Kenneth Matiba and Charles Rubia, openly expressed support for more political parties. Shortly thereafter, human rights lawyers complained of harassment by government security forces.

Last week, many of the most outspoken advocates of political change in Kenya were rounded up and jailed. Matiba, Rubia, human rights lawyers John Khaminwa and Mohamed Ibrahim, and Gitobu Imanyara, chief editor of a Kenyan law journal, were among those arrested in the days leading up to a pro-democracy rally that was tentatively scheduled, but canceled, by the former cabinet members.

On Saturday, a couple of hundred observers showed up at the rally site in Nairobi anyway, leading to riots and sporadic clashes between police and civilians in which dozens reportedly were hurt, none seriously.

There were more disturbances today in the capital, when thousands of people returned to the area where the rally was supposed to have been held. When police tried to disperse them, some threw large rocks. Riot police bearing clubs in surrounding neighborhoods occasionally fired tear gas to break up groups of people.

Most political detainees are held under a statute known as the Preservation of Public Security Act, which allows the government to hold suspects for as long as 14 days without charge or trial. The act is just one of numerous examples of human rights violations here raised by the international human rights group, Africa Watch.

"We are very concerned that a strong stance be taken by the Bush administration and Congress," said Joyce Mends-Cole of the group's Washington office. "We'd like them to publicly condemn all that is happening in Kenya."

The government regularly accuses the United States of encouraging discontent here and violating Kenyan sovereignty by demanding political change. One indication of the ragged state of U.S.-Kenyan ties was the front-page headline of an editorial in today's Kenya Times condemning criticism leveled by the U.S. envoy here. "Shut up, Mr. Ambassador," it read.