The West German government, fearing a serious backlash in public opinion over the deployment of new nuclear missiles, has urged the United States to halt military action in Grenada and withdraw its troops as soon as possible.

Foreign Minister Hans-Dietrich Genscher, speaking today in a special parliamentary debate about Grenada, expressed annoyance that Chancellor Helmut Kohl's government was not consulted prior to the invasion.

"Had we been given the opportunity to do so," he said, "we would have advised against the intervention because in all regions we advocate political solutions to conflicts, and not military ones."

Genscher indicated that the U.S. assault on the tiny Caribbean island could have troubling repercussions as West Germany prepares to deploy new U.S.-built Pershing II missiles, saying the "latest developments affect us both politically and psychologically."

After more than a week of peaceful demonstrations, top government officials said they now feared that violent protests could erupt if radical elements seek to justify aggressive actions by linking American intervention in Grenada with the imminent arrival of the Pershings.

"The worst disturbances have occurred in West Germany when protests were mobilized against symbols of so-called U.S. imperialism, such as the shah of Iran or Chile," one official explained. "Now the radicals can point to Grenada, and they may get more support for violent action against the missiles."

The Kohl government is still confident it can proceed to station the missiles if the Geneva negotiations on medium-range nuclear weapons fail, as expected, to achieve an agreement in the next few weeks.

The West German parliament, where Kohl's coalition holds a comfortable majority, is expected to give the green light to the missiles following a final debate on Nov. 21.

But the invasion of Grenada shows signs of intensifying the security dispute between the government and the opposition Social Democrats, who are expected to denounce the missile deployment at a party congress in mid-November.

Horst Ehmke, the Social Democrats' deputy floor leader, described the military action as "a violent breach of international law" and said it should be condemned as vigorously as Moscow's intervention in Afghanistan and the 1968 invasion of Czechoslovakia.

Ehmke stressed that the Reagan administration's support for the government of Philippine President Ferdinand Marcos proves that it "is not suitable for restoring democracy to Grenada."

Another leading Social Democrat, Hans-Juergen Wischnewski, bemoaned the lack of consultation with West European governments. "It's a black day for the alliance," he said.

Other legislators warned that West Germany was endangering itself by entrusting control of powerful new nuclear missiles on its soil to President Reagan.

Joschka Fischer, a member of the antinuclear Greens Party, called Reagan a "trigger-happy celluloid cowboy" and claimed that Chancellor Kohl would be committing "an abysmal act of political stupidity" if he allows the missiles to be deployed.

Chancellery and Foreign Ministry officials admitted that the heated rhetoric in today's debate may presage a resurgence in public concern about charges that the Reagan administration is too reckless in foreign affairs to maintain full responsibility for nuclear weapons based in West Germany.

They stressed that the issue of maintaining a "dual key" to nuclear weapons would not become a major controversy because West Germany solemnly renounced any intention of becoming a nuclear power years ago.

Rather, they are more worried that the arduous process of debunking fears that the Reagan administration might tolerate a limited nuclear war in Europe may be jeopardized by the invasion of Grenada.

Government officials also said they were dismayed that the administration did not seem to bear in mind the possible impact that such military action might have in West European countries in the climactic weeks before deployment.

"To say we are not happy about the timing of this invasion is quite an understatement," said a West German official.