Chancellor Helmut Kohl's government decided today to open formal negotiations with the United States on the terms of participation for West German companies in the Strategic Defense Initiative, President Reagan's research program into space-based missile defenses.

Government spokesman Friedhelm Ost announced that the West German Cabinet voted unanimously to send Economics Minister Martin Bangemann to Washington next month to seek improved conditions for the exchange of scientific research and technology between the two allies.

Kohl's center-right coalition, while reiterating its political support for SDI, also declared that it would not pursue any direct government role nor provide any public funding for the research effort.

By stressing the business aspects and muting the security repercussions of SDI, the Bonn government clearly hoped to stifle a drawn-out feud between Kohl's Christian Democrats and the junior partner Free Democrats over the wisdom of embracing the controversial space defense project.

The proposed agreement would be aimed at protecting the interests of West German businesses by setting out guidelines on patent rights, technology transfers and marketing arrangements, as well as pricing and secrecy rules.

The West German decision provoked angry criticism in Moscow. The Soviet news agency Tass charged that Bonn intended to use the "cosmic bridge" of SDI to "bypass existing bans and lay the path for nuclear arming" of the West German Army.

Bangemann is expected to hold talks with the Commerce and Defense departments. The Bonn government believes a draft agreement could be reached by the end of March "if both sides are reasonable," according to Horst Teltschik, Kohl's adviser on foreign and security affairs.

Earlier this month, Britain became the first country to sign an accord regulating the involvement of foreign firms in the SDI research program.

The so-called "memorandum of understanding" between London and Washington cites 18 areas where British technology could play a leading role in SDI research but makes no binding commitments. Britain was forced to drop an earlier demand for $1.5 billion in contract guarantees.

Before today's decision, the Kohl government hoped to examine the SDI pact that London signed as a possible precedent. But Britain refused to disclose its detailed contents, citing national security. Diplomats said a personal appeal by Kohl for a copy of the document was rebuffed by Prime Minister Margaret Thatcher.

West German officials said the Bonn government nevertheless appears ready to follow London's approach to the SDI cooperation issue, outlining the still-to-be-negotiated terms in a similar memorandum. On the other hand, an exchange of letters may prove sufficient, particularly because West Germany wishes to emphasize business interests and avoid the security questions that would involve the government, the officials said.

The decision today reflected the persisting conflict within the government over how closely West Germany should become involved in the controversial SDI project.

Kohl and other Christian Democrats have advocated a staunch political endorsement of SDI to demonstrate allied support for Reagan and to give him a stronger hand in the Geneva arms talks. Kohl also contends that West Germany must not miss out on any technological breakthroughs or spinoffs that result from the multibillion-dollar research program.

But Foreign Minister Hans- Dietrich Genscher and other members of the Free Democratic Party have expressed fears that an intimate role in SDI could damage Bonn's relations with Eastern Europe. Moreover, Genscher has expressed concern that future SDI development could nurture fresh doubts about whether the strategic fates of the United States and Western Europe are truly coupled within the NATO alliance.

Genscher is also known to loathe tampering with the alliance deterrence policy that has avoided nuclear conflict in the postwar era. Leading officers in the West German Army also have voiced apprehension that massive investment in a space-based antimissile system could siphon funds away from necessary improvements in conventional defenses along the East-West border.

Bangemann will seek to work out a framework for future cooperation that would encompass not just SDI but a complete range of trading activities involving high technology. West Germany has complained that tight U.S. restrictions on sensitive products have hampered its important commercial ties with the Soviet Union and other East Bloc countries.