WASHINGTON (AP) _ The U.S.-Soviet nuclear arms treaty has major military and political gains for the NATO alliance and should be approved without delay, a group of arms control experts told the Senate Foreign Relations Committee on Friday.

''The overriding question is whether it lessens the risk of nuclear war,'' said Paul. C. Warnke. ''By getting rid of a category of nuclear weapons that are particularly vulnerable and adapted for first use, the treaty admirably meets this test.''

Warnke formerly served as director of the Arms Control and Disarmament Agency. His testimony, along with the other three experts, concluded a third week of hearings by the committee, which is one of three in the Senate considering the pact.

The treaty also was criticized Friday by William Van Cleave, of the Hoover Institution at Stanford University. He told the panel that ''it is not in our interest.''

The accord was signed in December by Soviet leader Mikhail S. Gorbachev and President Reagan. It eliminates U.S. and Soviet nuclear-tipped missiles with a range of between 310 and 3,400 miles.

The administration has pushed hard for Senate ratification, which will require a two-thirds vote of the 100-member chamber. Senate leaders say approval is likely.

Warnke told the panel that ''from the standpoint of strategic policy, intermediate and shorter-range missiles fail to meet the basic criteria strategic stability.''

''Because of their areas of deployment, many of them are highly vulnerable,'' he said. ''Moreover, because of the shorter ranges involved, ballistic missiles in these categories can strike their targets within a few minutes and thus provide virtually no warning time.''

The treaty also offers political gains, Warnke said, because it shows the ability of the 16-member North Atlantic Treaty Organization to stand together and face down political opponents who opposed the U.S. weapons that were deployed starting in 1983, he said.

Ralph Earle Jr., policy director of the Lawyers Alliance for Nuclear Arms Control, a private group, echoed Warnke's comments.

''To discard the treaty now would undermine the solidarity and support the United States has received from our allies around the world,'' Earle said.

''What this treaty does is put arms control back on the track following a hiatus of eight years,'' he told the panel. ''It puts the signature of a conservative American president on an arms control pact, lending the process further credibility with the public and in Congress.''

''This treaty can, and should, be used to galvanize support for further reductions in conventional and strategic nuclear arms,'' Earle said.

Jonathan Dean, arms control adviser to the Union of Concerned Scientists, said the treaty ''has done more than any event of the past 40 years to promote a European feeling of responsibility for their own defense and for intra- European defense cooperation.''

The chief military effect ''is to improve NATO's theater-range nuclear position while enhancing crisis stability,'' Dean told the panel. ''Consequently , the agreement creates no new need to improve NATO's nuclear forces. It makes no sense to build down nuclear weapons with one hand and build them up with the other.''

William Schneider Jr., chairman of the U.S. General Advisory Committee on Arms Control and Disarmament, praised the treaty's verification provisions, which include short-notice inspections and on-site inspections.

He noted the Soviets' ''abysmal record'' of complying with past arms control agreements and noted the new treaty ''provides an important opportunity to begin to correct this problem.''

Van Cleave, criticizing the treaty, said he believes the main Soviet aim is to cripple Reagan's Star Wars anti-missile defense research program and other U.S. efforts aimed at building up western defenses.

''Virtually every western modernization program, particularly in the nuclear areas, would be greatly dampened by the current climate of arms control,'' he told the panel.