With a high-level Soviet delegation observing, West German Chancellor Helmut Kohl declared his full support in parliament today for the research stage of President Reagan's Strategic Defense Initiative, primarily, he said, because the Soviet Union has demonstrated its own extensive efforts in space weaponry.

In Bonn's strongest endorsement yet of the "Star Wars" space defense scheme, Kohl told the Bundestag that "the American research program is, in our view, justified, politically necessary and in the security interests of the west as a whole." He said that Bonn would soon open talks with Washington on joining the project.

Kohl cited an antisatellite test high over Munich in 1983 as evidence that the Soviets have pursued a sophisticated program of military space research. He used this example as a strong rationale for West Germany to join the reseach phase of Reagan's program.

Kohl's announcement that West Germany was about to begin talks with the United States on joining the research effort placed it well ahead of Washington's other European allies and appeared to advance Bonn's decision-making timetable on the issue. It followed by a day Norway's announcement that it wanted nothing to do with the project.

But Kohl insisted that West Germany must be granted a "fair partnership and guaranteed free exchange" of all findings that derive from the research program. He also reiterated his backing for a joint European approach to involvement in research on a space-based defense system in order to increase influence with the United States over future strategic and development decisions.

Kohl's speech today was designed to set forth a coherent government policy toward Reagan's proposal, which has evoked mixed feelings in Western Europe.

Some of the European allies have expressed eagerness to share in the fruits of the five-year, $26 billion research program but remain troubled by the long-term implications for Western deterrent strategy and a possible arms race in space.

Western diplomats said the favorable tone struck in Kohl's speech may have been intended to ward off a potential U.S.-European clash over the "Star Wars" program at the seven-nation economic summit in Bonn, May 2 to 4.

Kohl said today that he would discuss space defense research with Reagan, who will prolong his stay in West Germany until May 6 to pay an official state visit, but it still remains uncertain whether the participants at the world economic summit will agree on a joint declaration on weapons in space.

West Germany's decision to support "Star Wars" research, Kohl said, was motivated primarily by the fact that Moscow has been making "immense efforts" to develop space and antimissile defense systems for more than a decade.

Speaking to an audience that included a delegation from Moscow led by Central Committee secretary Mikhail Zimyanin, the chancellor said the Soviet Union "is the only country in the world which has useable antisatellite weapons, so-called killer satellites. We know that the Soviet Union carried out a test of such a system over Munich in summer 1983."

Sources in Bonn said it was known that the Soviets' antisatellite test was not a laser system, although the exact nature of the test was not divulged. It did not violate West German air space, they said, because it occurred at an extremely high altitude.

West German sources, indicating that information about the test came from U.S. intelligence sources, said U.S. officials are cautious about giving away such information for fear of revealing the nature of satellite reconnaissance.

Because of its own research into space weapons, Moscow's attacks on Reagan's project held "no credibility or moral justification," Kohl added. But he also appealed to the Soviets not to exploit the controversy to block progress toward reductions in nuclear weapons at the Geneva arms talks.

A senior adviser to Kohl said one of the key factors behind West Germany's endorsement of the reasearch is the conviction that the project brought the Soviets back to the bargaining table and thus might be intimidating enough to coax Moscow into an arms-control agreement that radically reduces the number of medium-range nuclear weapons based in Europe.

In a previous speech at a party congress in Essen, Kohl contended that space-based systems "could become increasingly superfluous" if the superpowers agree to deep cuts in nuclear missiles.

Despite his advocacy of the research, Kohl did not mitigate any of the earlier conditions that he has cited as imperative for West German participation in the project.

He insisted that the exchange of results during the research phase "must not be a technological one-way street" that benefits only the United States.

"We want to be able to look inside the black boxes, too," is how a top chancellery official explained Kohl's concerns.

The chancellor said a team of West German specialists would soon leave for the United States to discuss conditions for participation.

Kohl also rebuffed Defense Secretary Caspar W. Weinberger's call for the allies to decide on joining the project within 60 days, saying Bonn would "not let itself be put under pressure to reach a decision quickly but will ensure it has all the facts it needs to make a choice."

In promoting a common European line toward space-weapons research, Kohl said that a high-technology project of such magnitude was bound to yield "important and far-reaching results" in other fields besides defense.

He stressed that European industries were obligated to become involved if only to ensure that Europe "does not get left behind and become second-class."

The opposition Social Democrats, meanwhile, proclaimed their rejection of any role in Reagan's project.