A committee of the Episcopal Diocese of Washington has completed an ambitious and sweeping two-year study of war and peace issues, citing "the suicidal character of nuclear war," and concluding that deterrence is "the only acceptable purpose" for this nation's possessing nuclear weapons.

The 120-page report, entitled "The Nuclear Dilemma; a Search for Christian Understanding," opposes President Reagan's proposed "Star Wars" Strategic Defense Initiative as both technically unfeasible and strategically counterproductive because such initiatives "can only be a catalyst for a new arms race."

The report also concludes that claims for the MX missile "as a symbol of resolve or a bargaining chip are not credible."

Urging renewed efforts toward arms reduction agreements between the United States and the Soviet Union, the report calls on both parties to reject "attempts to achieve nuclear superiority," because "such a goal is beyond the reach of either superpower, and the quest for it engenders fears and fuels the arms race."

The 15-member Committee of Inquiry on the Nuclear Issue, appointed in June 1983 by Bishop John T. Walker, followed the pattern set by Roman Catholic bishops and took testimony from more than 40 experts from government, the military, academia and the church to help them reach their conclusions.

Among those who testified were Defense Secretary Caspar W. Weinberger; former arms negotiator Paul Warnke; U.S. Air Force Gen. David Jones, chairman of the Joint Chiefs of Staff under Presidents Carter and Reagan; Paul Nitze, former secretary of the Navy and deputy secretary of Defense, and Kenneth Adelman, director of the U.S. Arms Control and Disarmament Agency.

Walker launched the study as his response to a 1981 pastoral letter from the Episcopal bishops nationwide, calling on church people to work for peace and an end to the arms race.

The expertise of 12 lay persons and three clergy he appointed to the committee reflects the talent available in Episcopal parishes in the nation's capital for such a study. Chaired by Viron P. Vaky, former assistant secretary of State for inter-American affairs, the group included present or former government officials experienced in foreign service, the military, national security and arms control.

Like the Catholic bishops, the Episcopal committee rejected any first use of nuclear weapons on pragmatic as well as moral grounds. "Nuclear weapons have no useful military role," the report said. "Nuclear weapons generate risks out of all proportion to any rational goal."

But committee members could not agree on whether nuclear retaliation "might prevent a greater evil."

The report concedes that "to some degree deterrence inheres in the nature" of nuclear weapons, with each superpower inhibited by the certainty of nuclear retribution in case of an aggressive attack.

"But deterrence is not automatically stable," the report says. "Nations can miscalculate. Accidents, misperception, irrational responses in the heat of the crisis can all lead to a failure of deterrence."

The report dismisses the notion popular with some that the strategy of mutual assured destruction -- the certain knowledge that a nuclear attack would be countered by an equally cataclysmic counterattack -- will maintain the peace.

"Mutual assured destruction is not a strategy. It is a condition. It is, simply, the very likely consequence of any significant nuclear exchange," the report said. "No system or situation is satisfactory which cannot survive a single major mechanical or human failure."

The report came down hard on the continuing failure to achieve effective arms control, blaming in part the "lack of consistency and continuity in U.S. policy toward the Soviet Union. It appears that each new president thinks we must reinvent the wheel in arms control negotiations."

The report calls for an end to name-calling and "demonizing" in negotiations with Soviet Union, and a focus instead on the common threat of nuclear annihilation.

"We are under no illusion that such a task will be easy," the report said, citing the "adversarial and unbenign" stance of Soviet leaders, deep differences in values and purposes between the two systems, Soviet expansionism and the suppression of human rights.