Bonn — To many seasoned West German commentators, it is hard to believe how fast West Germany's Social Democrats have bounced back from their loss of power last year.
The irony is that, although rejuvenated, the Social Democrats may be happy to lose a national election on March 6, leaving the present Christian Democratic government to deal with the two key issues that rankle West Germans - economic austerity measures and the basing of American intermediate-range nuclear missiles to counter the massive buildup of Soviet SS-20 rockets.
Just four months ago, when Chancellor Helmut Schmidt was overthrown in a parliamentary vote of no confidence, the Social Democrats looked like an exhausted, demoralized, and divided party.
But under the new leadership of Hans-Jochen Vogel, and with a program that is noticeably more socialist with tinges of nationalism, the party seems more united, more dynamic, and more appealing to the public than Chancellor Helmut Kohl and his Christian Democrats.
Mr. Vogel's trips to Washington and Moscow, where he was received like a potential chancellor, have conveyed to many the impression that he cares more about disarmament than does Mr. Kohl. And his party has also picked up support from people who feel the new government has been redistributing wealth from the poor to the rich.
Vogel appears to have judged public opinion correctly when he shifted the Social Democrats' stance on NATO's nuclear rearmament plans. He put maximum emphasis on the need for a deal that would prevent the deployment of a single new US medium-range missile in West Germany, even though the government accuses him of abandoning Western security interests.
The Social Democrats' rebound has changed the political situation considerably.
Last fall, they had slid to less than 30 percent in the opinion polls, were split on both the economic and missiles issues, and rapidly lost the services of their biggest electoral asset, Mr. Schmidt. Herbert Wehner, the parliamentary floor leader who made the Social Democrats into a governing force in the 1960s, predicted on the night when Mr. Kohl won that the Social Democrats could face up to 15 years in opposition.
Now, however, the opinion polls show the Social Democrats back up to 42 or even 43 percent of the vote - not enough to win the election but perhaps enough to deprive Kohl of the absolute majority he seemed assured ofonly a few weeks ago. The polls also show that Vogel, a former justice minister, is more popular than Kohl.
So what has changed? Perhaps the most important factor was the Social Democrat's sheer sense of relief at casting off the burdens of government and the constant need to make compromises with the Free Democrats of Foreign Minister Hans-Dietrich Genscher.
The retirement of senior figures like Schmidt and Mr. Wehner has allowed the party to launch a process of rejuvenation in which it can take up new causes such as the environment and the growing antinuclear peace movement without having to be so pragmatic. Vogel has set the Social Democrats on a course designed to win back young voters who had drifted away to the radical ''Green'' party without sacrificing the Social Democrats' traditional working-class voters.
His policies, expounded under the nationalistic motto ''In German interests, '' seem more in harmony with the party than were Schmidt's. Both on the economy, with calls for more state intervention, and on disarmament, with calls for United States concessions to enable an agreement with the Soviets, the Social Democrats seem at last to be following their instincts and not the needs of survival in government.
Still buoyed by widespread public anger at the manner in which Schmidt was removed, the party has also benefited from the Kohl government's clumsy start. The Christian Democrats have puzzled many of their own voters by changing their minds against repaying a compulsory loan from the rich, and by arguing in public about the Western aim in disarmament talks with the Soviet Union.
But the question remains: Are the Social Democrats, after only five months in opposition, ready to govern again? The answer, though denied by party leaders in public, is no.
According to highly-placed sources in the party, Vogel realizes he cannot replace Kohl in March, and he does not want a coalition with the Greens, should they win the 5 percent necessary to take seats in the Bonn Parliament.
For the Social Democrats, the best solution would be a hung Parliament in which they would allow Kohl to be reelected as chancellor and demand policy concessions in return for supporting his minority government.
According to this strategy, Vogel would allow the Christian Democrats to bear the disgrace of deploying American missiles next December and coping with rapidly rising unemployment. He would use the Social Democrats' blocking powers in a hung Parliament to ensure there were no drastic cuts in the social welfare system.
The scenario ends with a parliamentary vote against Kohl sometime toward the end of next year in which Vogel would either have himself voted chancellor without having to form a coalition with the Greens or would force general elections if the prospects looked good for the Social Democrats.
Privately, most party leaders acknowledge that at least some of the US missiles will have to be deployed, and they would rather the Social Democrats were not associated too closely with that decision.