President Reagan last night pressed his proposal for a one-third reduction of U.S. and Soviet strategic nuclear warheads, rejected any revival of the abandoned strategic arms limitation treaty (SALT II) and said that "no useful purpose" would be served by a promise not to make first use of nuclear weapons.

In a prime-time news conference, Reagan said that the unratified SALT II treaty, which Democratic critics of his missile-reduction proposal have suggested making a starting point for negotiations with the Soviets, "simply legitimizes the arms race."

Afterward, deputy White House press secretary Larry Speakes said that Reagan had been prepared to say that "SALT II was dead" if he were asked about it -- an opportunity the president passed up when the question was actually put to him.

Reagan said that both the United States and the Soviets were abiding by monitoring provisions of the unratified treaty but declared that SALT II did nothing to reduce the power and number of the most "destabilizing" missiles.

In an opening three-minute statement on nuclear arms control the president tried to stick closely to the language of his arms control speech of last Sunday at Eureka College, an approach which featured a two-phase plan which would begin with reduction of U.S. and Soviet missile arsenals from 7,500 to 5,000.

White House advisers were disappointed at what they considered insufficient television coverage of the president's Sunday speech. As a result, they rescheduled what had been planned as an afternoon press conference to prime time -- only the second time Reagan has held an evening press conference during his administration.

Reagan repeated his statement of last Sunday that he hoped that Soviet President Leonid Brezhnev would reply to his negotiation offer soon and that talks could begin by the end of June.

When Reagan was asked how long it would take to negotiate a limit on warheads with the Soviet Union, he declined to make a forecast but took the opportunity to present his administration's military spending program as giving the Russians an incentive to negotiate.

"And the very fact that we have shown the will and are going forward on the rebuilding program is something that I think offers an inducement to the Soviet Union to come to that table and legitimately negotiate with us," Reagan said. "In the past several years, those negotiations took place with them having a superiority over us and us actually unilaterally disarming. Every time someone wanted a little money for another program, they took it away from defense. That isn't true anymore."

In other comments, Reagan said he was willing to negotiate reduction of U.S. bombers and cruise missiles but had focused on the intercontinental ballistic missiles because they were more destabilizing.

"What we are striving for," he said, "is to reduce the power, the number and particularly those destabilizing missiles that can be touched off by the push of a button."

Reagan made one error in discussing nuclear weapons capability. He said submarine-launched missiles can be recalled. They cannot.

Responding to a question about whether the United States should renounce the existing NATO treaty which envisions nuclear retaliation against the Soviets if they attack western Europe with conventional arms, Reagan said he didn't think "that any useful purpose is served in making such a declaration."

"Our . . . strategic nuclear weapons unfortunately are the only balance or deterrent that we have to the massive build-up of conventional arms that the Soviet Union has on the western front -- on the NATO front," the president said.

On other foreign policy issues Reagan said that "I have faith" that both Egyptian President Hosni Mubarak and Israeli Prime Minister Menachem Begin would seriously pursue the talks on autonomy for Palestinians living on the West Bank and the Gaza Strip. He declined to comment on an Israeli demand that talks should be held in Jerusalem.

Reagan said he also looked forward to renewing a strategic cooperation agreement with Israel that he suspended after Israel annexed the Golan Heights.

On the British-Argentine war over the Falkland Islands, the president acknowledged that the sympathies of South American countries "are more with Argentina than ours" but added that he didn't think there had been "irreparable damage" to U.S. relations with these nations.

Near the end of the news conference Reagan responded to a question that he was being criticized by "old friends" for turning "moderate and pragmatic" on issues after years of being considered "too bellicose and too hawkish on foreign affairs."

Reagan said his views hadn't changed, either on the Soviet Union or on war-and-peace issues. The Russians follow a different "moral standard," the president said.