WASHINGTON (AP) _ Five national church leaders were arrested inside the Capitol on Ash Wednesday in a protest over U.S. support of the Nicaraguan Contra rebels.

The five, dressed in black clerical robes and purple stoles, were led from the Rotunda by Capitol Police after ignoring warnings that they had entered unlawfully for the purpose of demonstrating in the Capitol building.

Supporters, who had attended a prayer service on the steps of the Capitol, sang a hymn, beginning, ''Were you there when they crucified my Lord?'' They repeated the chorus - ''Tremble, tremble'' - as the five were led away.

Participants in the prayer service held aloft cardboard crosses bearing the names, ages and dates of death of young victims of the war in Nicaragua.

United Church of Christ President Avery D. Post, one of the five arrested, told a news conference earlier, ''We are here today to bear in our bodies the humiliation of a nation that has misused power. We declare our complicity with policies that are inhumane.''

''The United States-sponsored war against Nicaragua was made in the U.S.A., directed and financed by the United States, and is being operated out of Washington today by people with government paychecks,'' Post said.

Others arrested as part of the ''Lenten Witness for Peace and Justice in Central America'' included Rev. Arie Brouwer, general secretary of the National Council of Churches; John Humbert, president of the Christian Church (Disciples of Christ); Father Joseph Nangle, justice and peace coordinator for the Conference of Major Superiors of Men, and Doris Anne Younger, general director of Church Women United.

Vigils in support of the protest action also were held outside U.S. embassies in Ireland and West Germany, Brouwer said.

''We are hoping to strengthen the hands of those in Congress who oppose the administration's policies,'' he said.

Congress, in the wake of the Iran-Contra affair, is considering withholding $40 million earmarked for the rebels until the administration can account for how past aid was spent.

The $40 million is part of a $100 million package approved last year. The Reagan administration has requested an additional $110 million for next year.

The Most. Rev. Walter Sullivan, Roman Catholic bishop of Richmond, Va., said at the news conference that despite millions in aid, ''peace remains an illusion in Central America.'' He called U.S. policy ''senseless, immoral, illegal and inhuman.''

Gordon Sommers, president of the northern province of the Moravian Church in North America, called for a negotiated settlement to the Nicaraguan conflict. About 80 percent of the minority Indian peoples on the east coast of Nicaragua are Moravians, he said, and many of those are fighting the leftist Sandinista government.