President Daniel arap Moi is to arrive in Washington Tuesday on a state visit that coincides with Kenya's emergence as a staunch ally and fairly new military client of the United States.

The former British colony in East Africa was one of the first African states to declare against going to the Moscow Olympics after President Carter made his appeal for a world boycott if Soviet troops do not leave Afghanistan.

President Moi went to some length to tell his people how independent his decision to pull out was, based he said, on nonaligned principles and the global interests of small states. He has subsequently told his officials that even if the United States changed its policy and decided to go to Moscow, Kenya would not do so.

The decision was significant because Kenya, with world-class distance runners like record-holder Henry Rono, is one of the few African nations whose athletes might have captured some medals in the games.

Kenya has recently diversified arms purchases from its traditional narrow dependence on the British to include major procurements of F5E jets and Bell helicopters from the United States.

The Afghan crisis, following on the loss of U.S. military influence in Iran, has suddenly given the quietly flourishing relationship between Nairobi and Washington a strategic dimension.

Kenya, along with Oman and Somalia, has been approached by the United States for military facilities to assist U.S. operations in the Persian Gulf. Although U.S. tactical aircraft would have to be refueled in air if they flew there from Kenya's Mombasa Airfield, this country alone is in a position to provide food and some other essentials for a potential U.S. military operation in the Indian Ocean.

Moi, at a press conference in Bonn during a visit that preceded his U.S. trip, said "it is not true that we have offered the United States a military base in my country. What we have done and will continue to do, is offer military facilities to that nation." The distinction is crucial, for this country's membership in the Organization of African Unity and the nonaligned movement.

All specifics on the facilities are being kept secret. Reliable informants say that they do not, at this stage, go beyond a discreet increase in the military personnel of the U.S. Embassy here and the provision of some kind of storage facility in Mombasa to hold spare parts.

Kenya, unlike some Third World allies of the United States, has no political prisoners. The 25 once held by President Jomo Kenyatta were freed by Moi following the Kenyatta's death in 1978. Even Oginga Odinga -- once Kenyatta's vice president but later a bitter enemy whom Kenyatta refused to forgive for his attempt to form a second party -- was recently brought back into the political fold and made chairman of the National Cotton Board.

Like President Carter, Moi comes from a rural, religious background. He belongs to the miniority Tugen tribe. He was a school teacher and, like all Kenyans who can, has bought land. The president goes to his farm on weekends.

In his year and a half in office he has sought to curb corruption and has clamped down on the smuggling of ivory and coffee.

Kenya, with a population of 15 million, remains one of the more prosperous of African countries but Moi is likely to ask American help with a foreign exchange crisis brought on by the increase in oil prices. The Kenyan oil bill has more than doubled from $130 million in 1978, according to Energy Minister Munyua Waiyaki. "We must either reduce our economic growth of borrow foreign exchange."

The second imperative on the Kenyan side is food aid. Serious shortages of corn, a staple here, are expected in April and rice and wheat are in chronic short supply.

In discussions of U.S. strategic needs in the Horn of Africa, the Kenyans can be expected to note that their northern neighbor, Somalia, has never renounced its claim to part to northern Kenya and that any U.S. rearming of Somalia would not be well received by Kenya.

But in opposing U.S. military aid for Somalia, the Kenyans will contend with the argument of the Somalis that they, with Soviet-backed Ethiopia as a hostile neighbor, could become the next Afghanistan.