President Reagan said yesterday that Moscow's top priority is to block deployment of new American intermediate-range missiles in western Europe. However, he described as "a rumor" reports that the Soviets had threatened to halt negotiations on long-range strategic missiles if the United States went ahead with deployment of the intermediate-range missiles in Europe.

"We have only heard that as a rumor. We have no report that that is an official demand of their negotiating" position, the president said at a news conference yesterday.

Reagan was responding to questions about an article in The Washington Post yesterday that quoted unidentified informed sources as saying that the Soviets had threatened to halt the strategic arms reduction talks (START) in Geneva if the United States begins putting new Pershing II and cruise missiles in western Europe.

The sources said that this threat was voiced during the second round of the START talks in Geneva that ended last November.

State Department spokesman John Hughes told reporters they "would be misled" if they believed such press reports.

Other officials privately confirmed yesterday that the Soviets had made remarks that may have implied a threat to break off the arms talks, but said there were differing interpretations among U.S. specialists about whether this amounted to an overt threat.

The sources for The Post's story also said that the Soviet threat to break off the arms talks was another illustration of the carrot-and-stick approach being used by Moscow to try to head off the U.S. European missile deployment.

Informed sources said previously that the Soviets threatened earlier last year to break off the Geneva negotiations aimed at limiting the intermediate-range nuclear forces (INF). This reported threat came during informal conversations at the INF talks.

The Soviet position is said to have subsequently changed because Moscow apparently believed there would be a bad public reaction at that time to such a move at the INF talks.