Eleven Roman Catholic nuns and one laywoman were arrested by Capitol police yesterday as they knelt praying in the Capitol rotunda to protest U.S. military and economic aid to "repressive" regimes in Central America.

The demonstration, which involved nuns from six religious orders, was also staged to mark the second anniversary of the slaying of four American women missionaries in El Salvador.

While several score of nuns stood with their banners for a noon prayer vigil on the east steps of the Capitol, for which they had obtained a permit, a smaller group gathered in the rotunda, where demonstrations are prohibited. The nuns told reporters they were participating in a "conscious act of civil disobedience."

The action, they said, was intended "to express deep opposition to the United States policy in El Salvador, a policy of economic aid and military assistance that strengthens unfairly the repressive government" of El Salvador as well as other Central American countries.

For nearly 40 minutes, the women knelt beneath the Capitol dome and recited prepared liturgies, sang hymns and prayed for victims of violence in Central America as well as the people of the United States, who, they prayed, would "call this government from a policy of hostility, fear and aggression to one of reconciliation and peace."

Then U.S. Capitol Police Capt. Michael P.E. Morrison stepped into their circle, read them statutes they were allegedly violating, and ordered them to disperse. Police closed the rotunda, ushering nonparticipants outside, and arrested the demonstrators, who were "extremely cooperative," according to Deputy Chief Gilbert Abernathy.

The nuns were charged with unlawful entry and released on their personal recognizance.