West Germany's conservative opposition parties late last night set the stage for the most colorful and potentially constroversial election campagin in Bonn's postwar history when they chose Franz Josef strauss, 63, to oppose Chancellor Helmut Schmidt in next year's federal elections.

The nomination of Strauss, a major figure on the right wing of West German politics for virtually all of the postwar era, is likely to present West German voters with the clearest choice ever between conservative policies and those of the center-left coalition that has ruled here since 1969.

Strauss is the minister president, or governor, of his native state of Bavaria an is also the long-time head of the Christian Social Union [csu] party that operates there. The CSU is the sister party with the vastly larger and generally more centrist christian Democratic Union [cdu], which operates in West Germany's nine other federal states.

For several weeks, the two opposition conservative parties, which have formed a parliamentary alliance for the past 30 years, have been torn by dissension. Strauss put himself forward in May as the candiate of his party while the Christian Democrats nominated another state governor, Ernst Albrecht. The two parties have always run a single candiate and, until now, it had always been a Christian Democrat.

Last night, however, a joint meeting of the parties' parliamentary deputies nominated Strauss by a 135-102 vote over the younger, moderate but less experienced Albrecht.

In effect, Strauss now has succeeded with his argument that the larger Christian Democrats were without the kind of strong, nationally known leadership necessary to do battle with the popular and respected Schmidt.

Opinion polls, however, show Strauss has little chance against Schmidt and some conservatives feel that if may be best to let Strauss fight the losing battle this time and save their moderate candidates.

Although Strauss is often portrayed as an ultra-conservative Bavarian Bogey-man, he is one of the most experienced and quick-witted politicians in West germany and an effective campaigner. His speechs are earth and hard-hitting, and, unlike most German politicians, he uses humor well. Strauss is also a cartoonist's delight with a proper Bavarian beer belly and a large head sunk into broad shoulders with no neck visibly connecting the two.

He is a former federal defense and finance minister but his critics see him as a demogogue, prone to let his sleeves-rolled-up Bavarian style get out of hand at the national level.

He has, in fact, been compromised and knocked down politically several times. In 1962 he had to resign as defense minister for having lied to parliament when he said he had nothing to do with a police raid on a magazine's offices.

Although Strauss' for the top position was bold for the smaller party of the conservative alliance, his selection was not surprising because of the generally weak state of Christian Democratic leadership.

The critics, including Schmidt, argue that a Strauss campaign will polarize west German politics into more extreme right and left views than ever before, scare the country's neighbors both east and west, and possibly splinter the stable party structure to which West Germans have become accustomed.

Strauss does not accept this.

"I don't care for my political career," he said during a recent interview in his Munich office. "What I do care for is the future of Germany and Europe and I think a change of leadership in Germany is required. For me, the decisive criterion is to get the socialists out of power in Bonn."

The "socialists" he refers to is the Schmidt-led, 10-year-old coalition of Social Democrats and the smaller Free Democratic Party. Although Schmidt is hardly a socialist, Strauss things the youth and left wings of Schmidt's party have excessive influence in shaping government police.

The conservatives, behind Christian Democrat Helmut Kohl, narrowly missed unseating Schmidt in 1976 and Strauss believes a harder-line campaign fought nationwide could have won. Yet, Strauss' strength outside Bavaria is marginal and it is hard to separate his own ambition and frustration from his distrust of Social Democrats.

This is expected to be his last shot and he probably sees it as his best. "To define me solely as a conservative is not sufficient," Strauss says. "a good policy is impossible without a conservative component. All of my background is from the Christian Social center. I'm a liberal, a conservative, a man with a European focus. Some people are so far left that they see the rest of the world as right wing."

Although Strauss opposed the way formed chancellor Willy Bradt handled Bonn's rapprochement with Eastern Europe, he says now that "treaties must be kept and I would respect them. But our approach to our East European neighbors must be free from illusion and prejudice and wishful thinking. Real detente is essential but it can be achieved and maintained only by maintaining defense preparedness and without unilateral concessions."

Strauss says his platform would also "undoubtedly accentuate" the idea of German unity, meaning East and West Germany. He sees this as not the old and "obsolete nationalism" that caused Germany so much trouble in the past, but rather "the right of our nation . . . the German nation . . . for self determination."

Wouldn't this frighten the Poles and others?

No, says Strauss, "if we manage to convince them that our fight for freedom is their fight and if we convince them that from German soil there will never more in history arise a military danger to their integrity and security."

Last year, Soviet leader Leonid Brezhney came to Bonn on an official visit and wound up spending more time with Strauss -- and seeming to enjoy it -- than with other opposition leaders.

"We understand each other very well, "Strauss says of Brezhnev.

"He attacked me and my political friends and said our policy was not constructive and I told him he was wrong, that we were serious and sincered. I told him detente in Europe was a good thing. . . but that it was impossible in the long run to practice detente in Euope and a policy of warmongering in Africa."

Strauss, who speaks English well and is a long-time supporter of the United States, has changed his views slightly. He is appalled at how he says he is portrayed sometimes in the United States.

To the United States, Strauss says, he would offer a foreign policy partnership instead of a slogan that says, "Let the Americans do the job, it's up to them and we don'dt like it."

"We should try to diminish our dependence on America and strength on America and strengthen our partnership in sharing the political burden with America."

The irritations of recent years in the Bonn-Washington relationship Strauss sees as an "inextricable jungle of opinion, events, prejudices and interpretation. Carter and Helmut Schmidt transmit on different wavelengths, yet it happens very seldom that only one side is guilty.

"I am not obsessed by the opinion that if I were to be in Helmut Schmidt's place everything would change suddenly for the better. But I think I have greater experience and a more deeply rooted knowledge of American, German, European problems," Strauss says. CAPTION: Picture, Strauss offers West Germans clear election choice.