In the wake of defeat in national elections last month, West Germany's Social Democrats are struggling to revive their morale and recapture public support by linking their party more closely than ever to the peace movement.

Faced with the prospect of a long period in opposition after sharing power for 15 years, the Social Democrats are trying to rebuild a left-leaning majority by moving into the vanguard of the campaign to halt deployment of Pershing II missiles on West German soil later this year.

But as diplomats and party moderates point out, it is a strategy fraught with risks. Already, the Social Democratic leadership is being accused not only of disowning former chancellor Helmut Schmidt's defense policy but also of shattering the consensus on security matters that the major political parties have shared for decades.

Moreover, unions that form a core constituency of the Social Democrats are skeptical about placing priority on an antimissile crusade instead of unemployment. In the March 6 election, many workers bolted the party to vote for the Christian Democrats in the belief they will prove more adept at coping with the country's economic troubles.

Despite those considerations, many Social Democrats believe the first step toward a political comeback involves regaining control of the left by coopting the nuclear and ecology issues that brought the counterculture Greens party into parliament last month for the first time.

Left-wing elements in the party insist that the creation of a new majority outside the Christian Democrat-Free Democrat coalition must begin with resistance to the deployment of new missiles. Recently, the party's decision to support the Easter antinuclear demonstrations showed that the left-wing forces may be gaining the upper hand in party councils.

As party moderates, personified by Schmidt, have lost influence, the Social Democrats have moved rapidly away from the North Atlantic Treaty Organization's "two-track" decision, which implies that deployment of the new missiles should proceed if arms control talks between the United States and the Soviet Union fail to achieve a compromise on medium-range nuclear weapons.

Leading disarmament experts in the party, such as Egon Bahr and Karsten Voigt, now contend that the basis of the two-track decision no longer exists because the Strategic Arms Limitation Treaty (SALT II) was never ratified. They say the party is no longer bound by the NATO decision and should propose alternative arms control ideas.

Lately, Bahr has advocated a one-year moratorium on missile deployment to relieve the negotiations of the year-end deadline. The governments in Bonn and Washington, however, say this would lead to further negotiating delays and only fortify a Soviet monopoly on medium-range nuclear missiles.

Other Social Democrats, such as Voigt and deputy parliamentary leader Horst Ehmke, have suggested that the United States should offer a compromise that drops deployment of the powerful Pershing II missiles, which they describe as destabilizing, first-strike weapons.

Oskar Lafontaine, a member of the Social Democrats' executive board and its most outspoken critic of U.S. nuclear policy, called the Pershings a tool of "decapitation strategy" and charged that first-strike weapons violate NATO's purpose as a defensive alliance.

The party's parliamentary leader, Hans-Jochen Vogel, has tried to mollify both wings of the Social Democrats by sticking with his formula that calls for a "radical reduction of Soviet missiles so that new western missiles are made superfluous."

But as the party moderates have faded, Vogel has conceded that the peace movement must be considered "federal comrades" and a natural constituency of the Social Democrats.

At a recent meeting in Nuremberg, he said the party must regain a foothold in "the social wickerwork of institutions." He emphasized churches, which have been active in the disarmament crusade.

However, Vogel alluded to warnings that the party may itself turn into little more than a left-wing protest movement. "We must not allow ourselves to lose contact with broad sections of the population and thus find ourselves in such isolation that would make it impossible for us to regain political power in the foreseeable future," he said.

Despite the evident drift toward an antimissile stance, the Social Democrats are not expected to adopt an official line on the deployment issue until a national party congress convenes in November.

The hiatus may cause further confusion and wrangling within the party, especially if the antimissile campaign heats up. Social Democrats may have to decide whether or not to engage in acts of civil disobedience that peace movement leaders say seem inevitable as deployment pressures mount.

The soul-searching over the missile issue is reminiscent of the way Social Democrats were compelled to rethink their foreign policy after election defeats in the 1950s.

During the era of Konrad Adenauer, the Social Democrats gradually abandoned notions of nationalistic neutralism and nuclear-free zones to embrace a full commitment to NATO and the western defense alliance.

The resurgence of those earlier ideas, as the Social Democrats nurse their wounds from their latest defeat, has raised new questions about the direction of the party in opposition.

"The situation of the Social Democrats is about what it was 30 years ago: alone, lacking orientation and going astray," wrote Guenther Gillessen in the Frankfurter Allgemeine Zeitung. "The best proof of their isolation were the sighs of relief over their defeat, especially from Socialist leaders Francois Mitterrand and Bruno Kreisky" of France and Austria.