The Council of Bishops of the United Methodist Church, spiritual leaders of the nation's second largest Protestant denomination, denounced yesterday any use of nuclear weapons and the Reagan administration's Strategic Defense Initiative, popularly known as "Stars Wars."

In a pastoral letter addressed to 9.2 million members of the church in the United States and 15 other countries, the bishops rejected the doctrine of nuclear deterrence, the linchpin of the United States' modern military policy, as "a position which cannot receive the church's blessing."

"We have stated our complete lack of confidence in proposed 'defenses' against nuclear attack and are convinced that the enormous cost of developing such defenses is one more witness to the obvious fact that the arms race is a social justice issue, not only a war-and-peace issue," said the letter adopted unanimously by the council.

"U.S. arms are now being purchased with food stamps, welfare checks, rent subsidies, Medicaid payments, school lunches and nutrition supplements for poor mothers and their children," the document states.

The bishops said "a clear and unconditioned 'No' to nuclear war and to any use of nuclear weapons." The letter, titled "In Defense of Creation: The Nuclear Crisis and a Just Peace," is believed to be the strongest statement any church group has made on nuclear war and has received widespread attention.

The United Methodist leaders go much further than the 1983 pastoral letter on nuclear warfare produced by the National Conference of Catholic Bishops. The Catholic prelates agreed to a "strictly conditioned moral acceptance" of a nuclear deterrence, as long as vigorous efforts to seek nuclear disarmament agreements moved forward.

However, a high-level committee of Catholic bishops is reassessing its support for a policy of nuclear deterrence.

Bishop C. Dale White of New York, cochairman of the committee that drafted the Methodists' pastoral letter, said, "We see no way in which the deterrence doctrine can receive the blessing of the church." Nuclear deterrence, he said, "has credibility only if we intend to use this weapon."

The United Methodist bishops called for a comprehensive ban on nuclear testing, "a multilateral and mutually verifiable nuclear weapons freeze and the ultimate dismantling of all such weapons," and "bans on all space weapons" to achieve disarmament.

The letter states that "it is not meant to be a consensus opinion of our church or a policy statement of our denomination on the nuclear crisis."

Rather, it continues, it is an effort by the bishops to "seek to lead the church in study, prayer and action related to this issue and this theme, using this document as a basic resource and guide."

Along with the pastoral letter, which is designed to be read in the churches, the bishops approved an 87-page document that details the rationale for the positions taken.

A church spokesman said that all 46 of the church's domestic bishops, most of the 15 overseas ones and a large number of retired bishops, who have voice but no vote, were present for the session.

Work on the documents has been under way for two years. Like the Catholic bishops, the United Methodists began with a series of hearings in which they sought the views of specialists in a variety of fields, ranging from Secretary of Defense Caspar Weinberger to astronomer Carl Sagan.

The entire Council of Bishops debated the committee's first draft six months ago at its meeting in Wichita, Kan. The final versions of the documents were adopted here yesterday after less than three hours of discussion. Most of the changes proposed here were editorial in nature.

"There was not agreement on all points," said Bishop Ole Borgen of Stockholm, president of the council, after the session. "But there was no dissenting vote in approving the basic thrust of the document."

Most of the debate concentrated on the pastoral letter rather than on the accompanying explanatory document. The letter is "the primary word of the Council of Bishops to the churches on the issue," said Bishop William B. Grove of Charleston, W.Va. "It should say what we mean. A hundred people will hear the letter read to every one who will give serious study" to the foundation document.

Just before the vote, retired bishop Roy Nichols of New York pointed out that the document failed to mention terrorism. The bishops approved Nichols' suggestion that the committee be empowered to add material indicating that "if nuclear weapons are legitimized, that will increase the likelihood they will be used for terrorism."

Media representatives from as far as Australia converged on this bustling community, which is rich in Revolutionary War memorabilia. Several hundred church members from the area crowded into the stark hotel ballroom for the debate and gave the bishops a long standing ovation when the unanimous approval was announced.

In a news conference after the vote, White emphasized that the bishops were speaking to the churches, not for them. "It is not an ex cathedra pronouncement of what United Methodists believe," he said.

Bishops, he explained, are "chief shepherds. We can never command consent or bind the consciences of our people."

To the charge that the bishops were "meddling" in politics, he replied, "We are citizens of the United States . . . . We have the right to speak; as citizens we claim that right. We are questioning the current policy of this nation."