MOSCOW--Mikhail S. Gorbachev told his people yesterday that U.S.-Soviet relations have improved, but it is still too early to talk about a fundamental change.

He told Soviet television viewers that differences over the U.S. "Star Wars" program for developing a space-based missile defense remain among issues that could halt further improvements in the superpower relationship.

The Communist Party chief addressed Soviet citizens on the results of his trip last week to Washington, where he and President Reagan signed an agreement eliminating U.S. and Soviet intermediate-range nuclear missiles.

Gorbachev, dressed in a gray suit and red striped tie, spoke for 20 minutes, a relatively brief period, at the beginning of the nightly news program Vremya.

"If one is firmly based on the facts and is not given to exaggeration, it is yet early to speak about a fundamental improvement of Soviet-American relations," Gorbachev said.

But he added that in Washington, his talks with Reagan and other American political leaders were "different, more constructive than before."

Gorbachev said differences over Star Wars, formally called the Strategic Defense Initiative, still could halt progress in U.S.-Soviet relations.

During the Washington summit and the period leading up to it, the Soviets toned down their sharp criticism of Star Wars, indicating a possible change in the Soviet position.

Gorbachev and Reagan have pledged to work for a 50 percent cut in their long-range nuclear arsenals but the Soviets have made that agreement contingent on limits on testing and deployment of Star Wars, which the Soviets claim is banned under the 1972 Anti-Ballistic Treaty.