Chancellor Helmut Schmidt and NATO gained time but little else last week when Schmidt's Social Democratic Party rejected a proposed freeze on the planned deployment of new nuclear missiles in Europe.

The vote taken at the party's national convention represented more an expression of hope in future U.S.-Soviet negotiations on reducing such weapons than an endorsement of the missile plan. There was no party promise to accept the weapons should the talks in Geneva fail. Instead, party delegates agreed to reconsider the matter next year.

The vote suggests that West Germany's ruling party is attempting to play a special role between the superpowers, holding open its options in order to pressure not only the Soviets but also the Americans to bargain seriously.

"If we say we will station the weapons in any case, then the Americans no longer have any need to negotiate in Geneva," said Egon Bahr, the party's disarmament expert. "And if we say we will not station in any case, then the Soviets have no need to negotiate."

Arguing against a moratorium now, Bahr offered left-wing Social Democrats two concessions that could haunt Schmidt and NATO later. He said that if the Geneva talks were not completed by the time the stationing is due in December 1983, but an end seemed in sight, he would back a limited freeze of "four or five months" on deployment.

He also welcomed calls to debate a "new defense strategy" that would review NATO's longstanding concept of a mixed nuclear-conventional force deterrent and the doctrine of "flexible response," under which the West retains the option of using of tactical nuclear weapons to respond to a conventional Soviet attack on Western Europe.

This seemed to move the party closer to the demands of Erhard Eppler, a Social Democratic leader of the antimissile campaign, for "new fundaments" in Western security policy.

Apart from nuclear weaponry, the focus of West Germany's political debate in the coming months is expected to be on overcoming the highest unemployment rate in 29 years without stretching state spending beyond its limits.

The party convention planted the seed for more controversy--and for the possible fall this year of Bonn's left-center coalition government--by backing new spending and tax increases. Hans-Dietrich Genscher, chairman of the Free Democratic coalition partner, said his party would oppose more state intervention in the economy and regarded the Social Democratic tax plan as impractical.

Clashes over how to deal with West Germany's jobless, who now number 1.8 million or about 8 percent of the work force, have twice in recent months nearly brought goverment parties to a break. Last autumn, consolidation of the federal budget almost split the coalition, and in February an agreement on a $5.3 billion investment program was reached under pressure of a parliamentary vote of confidence called by Schmidt.

Genscher might already have switched his allegiance to the opposition Christian Democrats had it not been for the fact that the conservatives themselves appear in no hurry to take on the burden of government before the 1984 general election. In addition, Genscher cannot be certain whether his marginal party would survive losses of left-wing members that could come if he sought a union with the conservatives.

Analysts are watching state elections in June in Hamburg and in September in Hesse as national tests of voter confidence in the Bonn parties. They say the results could lead to a split of the coalition.