Paul H. Nitze, chief U.S. negotiator in talks with the Soviet Union on limiting nuclear missiles in Europe, warned the Soviets yesterday that if they want an agreement they should offer better proposals and stop threatening U.S. allies and trying to divide the North Atlantic alliance.

Nitze, in answering questions at a White House news conference yesterday, also suggested that there would be some "give" in the officially rigid U.S. position at those negotiations if the Soviets come forward with those better proposals.

Although the Reagan administration routinely has taken a hard line toward the Soviets on arms issues, a warning from Nitze may be more significant than others because he is widely viewed as the leading advocate for arms control within the administration.

Furthermore, Nitze is also the official who, along with his Soviet counterpart, actually worked out some unauthorized but possible compromises in the U.S. and Soviet positions last year. Even though those compromises were rejected eventually, Moscow knows he is a key factor if the current deadlock is to be broken.

His public warning also comes as the administration is launching a major effort to blunt Soviet attempts to influence public opinion in western Europe against NATO plans to deploy new U.S. nuclear missiles there unless Moscow dismantles hundreds of missiles it has aimed at western Europe.

Nitze met with reporters after an hour-long meeting with President Reagan and other top officials in which Reagan gave a personal send-off to his arms negotiators returning to Geneva for what Reagan called "a particularly important" round of negotiations.

In addition to Nitze, who heads the talks on Intermediate-range Nuclear Forces (INF) that resume Jan. 27, Reagan also met with retired Gen. Edward Rowny, who will resume Feb. 2 the Strategic Arms Reduction Talks (START) on limiting intercontinental-range missiles and bombers.

Joining the White House discussion was Secretary of State George P. Shultz, who is expanding his role in overseeing arms control policy in the aftermath of Reagan's firing earlier this month of Eugene V. Rostow as head of the U.S. Arms Control and Disarmament Agency. A number of informed sources have said plans to remove Rostow were in the works a month ago in order to make room for a larger Shultz role.

Reagan's nominee to replace Rostow, Kenneth Adelman, also was at the meeting, along with Vice President Bush, Defense Secretary Caspar W. Weinberger and White House national security affairs adviser William P. Clark. Bush will travel to seven European capitals beginning Jan. 30 as part of the effort to counter Soviet moves and to sound out allied views on the arms talks.

Reagan yesterday reaffirmed his "determination to explore every possibility" for working out "equitable agreements to reduce the arsenals" of nuclear weapons of both superpowers.

The INF negotiations on reducing medium-range nuclear missiles in Europe are the most "time-urgent," as Nitze said yesterday, because the NATO allies are scheduled to begin deloying the first of some 572 U.S. Pershing II and cruise missiles this December if agreement is not reached with the Soviets before then.

The Soviets also have linked their START proposals for reductions in long-range nuclear missiles to cancellation of deployment of the new Pershing and cruise missiles. Because they could reach the Soviet homeland from western Europe, Moscow considers them strategic weapons while Washington does not. It is widely assumed that there can be no START agreement without an INF agreement first.

Reagan reaffirmed that he was sticking to his basic proposals in both negotiations. This includes the "zero option" for medium-range missiles in Europe, which requires dismantlement of about 600 Soviet missiles in return for no deployment of the new U.S. missiles.

There has been pressure here and abroad for the United States to modify that position, which the Soviets have already rejected and which some arms control advocates believe will not lead to an agreement. The U.S. and NATO view is to hold fast until Moscow offers better compromise proposals.

After stressing that he had Reagan's full authority to probe vigorously for any give in the Soviet position, Nitze, under questioning, started to say that the United States was more flexible than its official position. But he caught himself and rephrased his answer.

"There will be give, if the Soviets come forward . . . ," he first said. But then he asked to change that to say "if the Soviet side gives, I'm sure we'll give serious consideration to any serious proposal" Moscow makes.

He said he would not answer a direct question as to whether the United States is locked into its zero solution.

Nitze's warning to Moscow came in a prepared statement. "So long as Soviet proposals continue to mask a desire for a dangerous military advantage," he said, "so long as Soviet pledges of peace are accompanied, not by cooperation at the negotiating table but by thinly veiled threats against our individual allies, we in the West must adhere" to existing policy.

Nitze, who will stop in Bonn and Brussels to brief allies en route to Geneva, also said he hopes the Soviets "will see the folly of seeking to divide and intimidate our alliance."

Nitze and Rowny also confirmed that Moscow, at various times in the past year, has said that if there is any movement toward actual deployment of the Pershing and cruise missiles in Europe the Soviets would have to "reassess their position" in the START talks.

When the Soviets were asked what that meant, Nitze said, "they said that might well include calling off our talks the INF negotiations , calling off the START talks" and taking other measures. But Nitze added that the threat "doesn't necessarily mean they will do it."

Rowny, saying he remained "guardedly optimistic" about eventual success for the START negotiations, added there is a possibility of an earlier agreement among the superpowers on new "confidence-building measures" to reduce the risk of accidental nuclear war.

He surprised reporters by saying his optimism was due partly to the fact that "one of the things the Soviets admire about this president [Reagan] . . . is his consistency" in not shifting positions from one proposal to another.

The Soviet delegates say, according to Rowny, "We know we can do business with a man who knows what he wants and can stay the course," a phrase that sent moans through the briefing room because it is Reagan's slogan for holding fast to his domestic economic plan.