Franz Josef Strauss, the West German archconservative, was on a podium in this southern commercial city confronting a marketplace crowd angrily split in its feelings toward what he stands for.

A jarring chorus of hisses and whistles, and placards that read "Boo" and "Forward into the '50s," drew white-helmeted police into the main market square downtown to quiet ranks of protesters as the Bavarian premier began to speak.

Polarization. Confrontation. These are the reference terms for West German politics today, and Strauss, whose bullish form, headstrong actions, and outspoken advocacy of a strong defense posture, modern technology and law and order has long provoked centrist and left-wing German voters, is preparing again for national poltical combat.

Virtually assured of reelection Sunday as the leader of the state of Bavaria -- a predominantly Roman Catholic, conservative region that, outside of a few Social Democratic strongholds such as parts of Nuremberg, genuinely reveres him -- Strauss used the Nuremberg platform this week to voice worries about a growing rift in West Germany.

His target was Willy Brandt, the Social Democratic chairman and former chancellor, who Strauss expects will try, now that the Social Democrats have lost power in Bonn, to shift the party to the left to attract young voters moving to the radical Green protest movement.

"I warn against a poisoning of the political atmosphere in the Federal Republic from Brandt's left cartel," Strauss bellowed. "I warn against a polarization, against a confrontation in which the democratic consensus can get lost.

"I can already see the slogans that will be used in the coming federal election campaign," he went on, referring to the promise of new elections next year made by the right-center coalition of Chancellor Helmut Kohl, who took charge in Bonn last week. "The left-wing radicals will roar with the tempting, diabolical and poisonous slogans favoring the social welfare state and peace and opposing capitalism and war."

In West Germany's tense political climate, the campaign strategy that the 67-year-old Bavarian boss eventually adopts could well have an important influence on the outcome.

After a drubbing in 1980, when his image as a potential warmonger and the tag brillant-but-uncontrollable cost him a drive for the chancellor's office against Helmut Schmidt, Strauss clearly has returned as a force to be reckoned with. He has been pictured on national magazine covers as an ominous shadow looming over Kohl and as the knave behind Bonn's new king.

Strauss has irritated the Free Democrats, beating unmercifully on their small, centrist party for abandoning Schmidt too late in the game.

He resents that they chose not to switch to his side two years ago, and now their participation in the new coalition blocks his own desire to be the dominant partner to Kohl. Strauss chairs the Christian Social Union, the Bavarian sister party to Kohl's Christian Democratic Union.

If he keeps up his attack, charging that the free-market oriented centrist party shares responsibility for the errors of the past 13 years of left-center government in Bonn, he could help push the Free Democrats out of the federal parliament. This would damage Kohl's chances of remaining chancellor, since it is a long shot that the conservatives will win an absolute majority.

Strauss may decide to soften his blows against the Free Democrats after the Bavarian election this weekend. In an interview in his car driving into Nuremberg Wednesday, he explained that his denunciations have been partly election-related. He had not wanted his party to be affected during the campaign by the "anti-Free Democrats" feeling among many voters stemming from what is widely viewed as the "disgusting" way the centrist party rapidly changed coalition partners.

The Social Democrats in Bavaria have been hitting the Free Democrats hard for their "betrayal" in hopes of gaining a Schmidt sympathy factor and mobilizing the party, which appears to be why Strauss has decided to distance himself from the Free Democrats.

State politics were not his only consideration. A reconstituted, and presumably weaker, Free Democratic Party, one controlled by its right wing and shorn of its chairman, Hans-Dietrich Genscher -- who holds the jobs of foreign minister and deputy chancellor Strauss covets--would suit well the Bavarian leader's national designs.

He said he welcomed cooperation in Bonn with "a classical liberal party." At the same time, Strauss doubted that the Free Democrats, whose parliamentary group was split about three to two over the switch to Kohl, could reunify themselves at a national party congress in Berlin Nov. 5.

Kohl, in contrast to Strauss' aggressive tactics, appears interested in helping dissident Free Democrats warm to the new coalition. So far, he has adopted moderate foreign and economic policies. Keeping the Free Democrats is useful to Kohl as a balance to Strauss and as a guarantee of a long-term national majority for the new government.

Asked if he saw himself at odds with Kohl on this point, Strauss replied with a grin: "I think it's good in a coalition to break down the tasks."

He said he was more concerned about strengthening the conservatives' own majority than rescuing the Free Democrats, despite the real danger that a hung parliament could result if Genscher's party drops out and the Greens enter after the next election.

What Strauss seems to be figuring is that if the Social Democrats do try to slide to the left to embrace the Greens in search of a new, left-of-center majority, this will open an opportunity for the conservatives to collect instead an absolute majority to the right of the center.

"The Social Democratic Party is risking serious internal tensions and could lose more voters to us," Strauss said. "The working class in Germany has nothing to do with the Greens, or with the ecologists, or with the alternatives."