In a world of unholy alliances, the United States has few Third World friends as respected in their own country, region and the world as Abdou Diouf, the president of Senegal, who is visiting Washington this week. As the Reagan administration moves against Libyan incursions into Chad, Diouf can offer important advice based on his experience as "point man" in resolving African crises.

Three months ago Diouf prevented the Organization of African Unity summit from breaking up over a dispute about the Western Sahara. Two years ago Diouf's troops moved into the neighboring Gambia to put down a coup attempt against its president while he was attending Prince Charles' wedding in London. Senegalese troops have remained in Gambia with President Diawara's consent, and a flawed confederation of the two countries has been formed to shore up the economic and political frailty of Gambia.

In the three years since President Leopold Senghor took the unprecedented step of voluntarily turning power over to his handpicked successor, Abdou Diouf has established a reputation for fairness, intelligence and honesty unparalleled in Africa. Diouf was the runaway pick as the best African leader in a recent continent-wide survey of journalists, academics and other officials published in Jeune Afrique magazine.

While exerting an international influence disproportionate to the feeble power of Senegal's faltering peanut economy, Diouf has maintained internal stability through an Islamization and democratization of what is already one of Africa's most democratic countries. He established closer relations with Saudi Arabia, responding to the 95 percent of Senegal's population that is Islamic and felt not fully recognized by the Catholic Senghor. His democratic opening has expanded political parties from the four allowed under Senghor to the present 14. There are 32 newspapers and magazines representing the range of political expression. The Politician, an intelligent monthly journal satirizing the government in cartoons as well as articles, would not exist in most developing countries.

The voters approved of Diouf's new policies in a February election that was one of the few multi-party elections in Africa. In a five-candidate race relatively free of voting irregularities, Diouf handily won the right to serve as the country's president for the next seven years.

Diouf's international stature and domestic democratic mandate are even more unusual when viewed in light of Senegal's meager natural resources, a history of negative average annual growth since independence, a GNP per capita of $430 a year and the second worst literacy rate in the world, according to the World Bank.

It is precisely because of his national and international popularity that Abdou Diouf could lead a bloc of African countries to condemn and isolate Libya within the African community. This effort certainly does not have to appear an American campaign even if the Reagan administration pushes it forward.

There is no love lost between Diouf and Col. Muammar Qaddafi. Senegal is friendly with almost everybody, including the PLO and North Korea, but Libya is often villified in the Senegalese press for its support of rebel forces in Chad or the Polisario guerrillas operating in the Western Sahara. When the Senegalese put down the Gambian coup two years ago, they blamed the Libyans for the uprising, but "there hasn't been a shred of evidence to prove Libyan involvement," according to a Western official in Dakar. For Diouf to lead such an anti- Libyan move might open him to charges of being an American puppet. But his recent mandate and his unusual blend of popular Islamic democratization guard against any immediate challenge, Islamic or otherwise, to his government.

A far greater threat to Diouf and the promotion of Western political ideals and interests that he represents could come in the Trojan Horse of foreign aid. In Washington, Diouf will be seeking an increase in U.S. and multilateral assistance to alleviate Senegal's massive external debt. Because of its stability and democratic traditions, Senegal has been a favored recipient of Western, especially French, foreign assistance, receiving $95 per capita, about twice the African average at current levels. This privileged position has led to profligate spending, an enormous bureaucracy and a debt burden exacerbated by large private bank borrowings in the 1970s. With an external debt of $1.5 billion, almost one out of five dollars spent is borrowed. This position might be tenable for a developing country with a large industrial base, but not a country of 6 million in which over 50 percent of foreign exchange is gained through agricultural exports--mostly peanuts selling at a world price below the cost of production.

The United States has not increased its assistance to Senegal from last year's figure of $36 million and threatens to withhold $20 million in balance of payments support this year unless Senegal remains in good standing with the International Monetary Fund. Diouf will prod President Reagan to free up these funds and to lobby for Senegal in the IMF. But Senegal is too bright a beacon of stability and democracy in the Third World for the United States, France and other Western donors to reward fiscal irresponsibility simply for short-term foreign policy gains. The developed countries share fundamental political values with Senegal that can be carried forward well into the future by its 47-year-old president. However, to ensure that he will continue that leadership role, he should match our assistance with fiscal discipline and real economic development.