The Reagan administration is considering an interim application of the proposed "Star Wars" missile defense system to protect European allies against Soviet short-range tactical nuclear weapons, a senior U.S. defense official said tonight.

In past efforts to enlist NATO support for a space-based nuclear shield, Defense Secretary Caspar W. Weinberger has emphasized its potential for defending Europe against incoming Soviet intermediate-range nuclear missiles, specifically triple-warhead SS20s.

The latest suggestion, which Weinberger is expected to underline at a two-day meeting of NATO defense ministers here, is to deploy the same kind of defense against tactical nuclear missiles, which have smaller payloads and shorter ranges than the SS20. Although the official did not discuss it, a ground-based fast-firing gun is one idea under study by the Pentagon.

The senior defense official, who spoke on condition of anonymity, said a defense against such Soviet tactical missiles as the SS21, SS22 and SS23 could be developed faster than the more complex system designed to destroy long-range ballistic missiles.

A tactical nuclear defense, he said, could be developed without violating the 1972 U.S.-Soviet treaty limiting antiballistic missile (ABM) defenses.

Some European leaders support the research phase of President Reagan's Strategic Defense Initiative (SDI), as Star Wars is formally known, but have expressed broad concerns about the potentially destabilizing effects of a move beyond that into development and deployment contrary to the ABM pact.

Weinberger, who reportedly is anxious to line up a unified Western front during the U.S.-Soviet arms control talks in Geneva, is expected at the NATO meeting to emphasize the consistency of a tactical nuclear defense with the ABM treaty.

"European carping will not strengthen our hand in Geneva," the official said. "But I think the President is quite determined to continue the American SDI program."

The official said European officials at the nuclear planning-group meeting will be reminded of the potential business interest for their countries in joint research of a tactical nuclear defense.