Pope John Paul II'S familiar white robes mingled with the gold vestments of a Greek Orthodox archdeacon, the red velvet-banded academic robes of Protestant clergy and the military-style uniform of the Salvation Army in an unprecedented ecumenical prayer service here yesterday.

At the pontiff's request, more than 200 leaders of other Christian bodies gathered here in the Trinity College chapel to pray with him for continued progress ih lowering the barriers that separate Christians of differing traditions.

"It is important that every individual Christian search his or her heart to see what may obstruct the attainment of full union among Christians," John Paul told the gathering.

The pontiff noted that in the United States, cooperative religious efforts already have led to "joint witness in the defense of the rights of the human person, in the pursuit of social justice and peace, and in questions of public morality."

He called for "continuing creative ecumenical action" to foster esteem for "the sacredness of marriage and the support of healthy family life as a major contribution to the well-being of the nation."

The meeting, attended also by some Jewish and Islamic religious leaders invited as special guests, marked only the second time in history that a pope met with a large number of non-Catholic Christian leaders, according to Cardinal William Baum. Pope Paul VI visited the headquarters of the World Council of Churches in Geneva in 1969.

John Paul's ecumenical gesture was an apparent success.

"One couldn't help but be moved that here was a pope singing with Protestants a Calvinist hymn -- and a hymn of Charles Wesley, one of the founders of Methodism," observed Claire Randall, general secretary of the National Council of Churches. "This was a witness of how far we have come."

Washington Episcopal Bishop John Walker called the service a "very positive step."

For the Rev. John Steinbrook, pastor of the Luther Place Memorial Church here, the impact of the ecumenical meeting was more personal. "It was beautiful," he said of the service.

Steinbrook, who said his Lutheran congregation yesterday took up a special offering to help the Catholic archdiocese defray the cost of the pope's Washington visit, was impressed particularly by the pope as a person. "That man reminds me of my father," who immigrated to this country from Germany, he said.

"My father went through the wars of Europe too, before he came to this country . . . . The pope, that good man, and my father would have been in the trenches opposite each other," Steinbrook reflected.