The spiritual leader of more than 250 million Orthodox Christians opened his first visit to the United States yesterday saying, "All free peoples are debtors to the American nation."

Dimitrios I, the ecumenical patriarch of Constantinople, presided over an Independence Day doxology, or thanksgiving, service at Saint Sophia Greek Orthodox Cathedral in Northwest Washington.

The 75-year-old leader is considered first among equals of the partriarchs of several churches, including the Polish, Bulgarian, Albanian, Russian, Romanian, Ukrainian and Greek Orthodox churches. The churches make up the second-largest Christian body in the world.

While most Orthdodox Christians live in Eastern Europe and near the Mediterranean, more than 6 million live in the United States and about 50,000 live in the Washington area.

Dimitrios's trip to Washington, which is to include a July 12 meeting with President Bush, will last 12 days. It is the first time an ecumenical patriarch, who traditionally resides in Istanbul, has visited the United States.

On Sunday, he will open the 30th Biennial Clergy-Laity Congress of the parishes of the Greek Orthodox Archdiocese. Monday night, he and several local clergy will lead an "Ecumenical Doxology of Peace" at the Lincoln Memorial. Later in the week, he will lay a wreath at Arlington National Cemetery and meet with congressional leaders.

On July 13, he will travel to New York, where he will meet with Mayor David N. Dinkins and United Nations Secretary-General Javier Perez de Cuellar and visit Ellis Island. His monthlong U.S. visit will also take him to Allentown and Johnstown, Pa.; San Francisco; Chicago; Buffalo; and Boston.

As Dimitrios entered Saint Sophia cathedral yesterday, about 100 people lined the steps, applauding and waving blue and white flags representing the archdiocese and the patriarch. Inside, many of the 800 people who filled the cathedral brought cameras and snapped photographs of the leader.

Dimitrios wore a burgundy and gold neckpiece called an omoforo. On his head was an epanokalimafhon, a cylindrical black headpiece with a black veil.

He spoke in Greek, and his remarks were translated into English by Father Leonidas Contos, a Greek Orthodox priest from Berkeley, Calif.

"Thanks to the creation and progress of the American commonwealth," Dimitrios said, "human rights have been, and continue to be, safeguarded wherever and for whatever reasons they are threatened."

A 250-member choir in the back of the cathedral led the congregation in "America the Beautiful" and "Battle Hymn of the Republic."

Father John Tavlarides, dean of Saint Sophia, said that more than 200 parishioners spent the last six months "cleaning, painting and sprucing up the cathedral to make it as near perfect as it can be" for Dimitrios's arrival.

"This is an amazing event," said Juliana Blome, a 25-year-old Orthodox Christian from Arlington. "It's very emotional because you hope the church will find more unity."