Pope John Paul II issued a strong denunciation of the holding of hostages yesterday as three American clergymen announced their acceptance of an Iranian invitation to visit the 50 Americans held captive in Tehran on Christmas Day.

The three clergymen to leave tonight for Tehran include the Rev. William Sloane Coffin of the Protestant Riverside Church in New York City, Bishop Thomas Gumbleton of Detroit, representing the U.S. Catholic Conference, and the Rev. William M.Howard Jr., president of the National Council of Churches.

A spokesman for the National Counsil said the three were invited by the Iranian Foreigh Ministry, with an approval of Ayatollah Ruhollah Khomeini's Revolutionary Council, "to administer their pastoral functions" to the hostages on Christmas.

The pope, in his annual "state of the world" address to the Roman Catholic cardinals, said the holding of the hostages is in "violation of unquestionable principles of international law, causing immense suffering to the persons concerned and their families."

While the pontiff did not specifically mention Iran, his target was clear and a State Department spokesman said, "We very much welcome the pope's undertaking and hope it will be heeded by those who hold the hostaged."

Spokesman David Passage added that while the U.S. effort over the last seven weeks to free the hostages has included contacts with the Vatican, the United States took no role in yesterday's initiative.

Passage expressed skepticism that the proposed Christmas visit by the clergy -- approved Friday by the students holding the Americans -- would take place, "given the past history of hopes being raised and then dashed."

In any case, he said, the clerics' visit "should not distract attention from the fact that the hostages are being held . . . in direct contravention of every principle of international law and human decency."

According to the National Council of Churches spokesman, the three clergy will issue a statement before departure from Kennedy International Airport this evening. They were unavailable for comment yesterday.

Another six clergy left last night for Iran. According to the Rev. Jimmy R. Allen, immediate past president of the Southern Baptist Convention, they hope to see Khomeini during a two-week stay. However, this group apparently has not been invited to visit the hostages.

The pope, in his wide-ranging address reported by news services from the Vatican, made a strong plea for observance of human rights and also condemned spiraling oil prices.