Beginning in 1987, two shuttle flights a year will carry experiments for President Reagan's so-called "Star Wars" antimissile research program, Michael I. Burch, assistant secretary of defense for public affairs, said yesterday.

The initial experiments will "test the ability to detect, track and aim against targets" in space, Burch told a Pentagon news conference. The technology is being tested two years earlier than originally planned, he said.

Sources said the tracking and targeting parts to be tested from the shuttle were developed in a Pentagon research program called Talon Gold that antedates the Reagan administration.

According to these sources, the tests include:

* A mounting device for attaching the telescope-like sight to the shuttle. This hinge-like piece has to be precise, one source said, because it must steady a viewer that will be aiming a distance equal to that from San Francisco to Washington, D.C.

* Sensors that can pick up, at the same distance, "the signature of objects" such as the "booster plume of a missile," one official said.

Earlier this month, Defense Secretary Caspar W. Weinberger told Congress that Lt. Gen. James A. Abrahamson, director of the Strategic Defense Initiative program (dubbed Star Wars), was restructuring the Talon Gold program with "a more comprehensive acquisition, tracking and pointing development program."

The shuttle test of the main, telescope portion of the system, set for 1989, has been canceled, though sources said land-based tests would be continued, and a more capable telescope developed.

Meanwhile, Weinberger said that congressional budget cuts in the Star Wars program last year will result in a one-year delay in demonstrating the integrated system.

Burch yesterday quoted Abrahamson as saying that "because things are going along quite well," the initial testing "can be accelerated." One Pentagon source said Abrahamson had decided to test "smaller bits" of the Talon Gold program to get "some results sooner."