Extremists Gain in W. Germany. POLARIZED VOTE

THE growing polarization of West German politics is rattling the center-right government of Chancellor Helmut Kohl. Recent state and local elections - including this weekend's vote in Frankfurt - show a surge by small right- and left-wing parties. If the trend continues, say West German analysts, the Bonn government could be replaced by a leftist coalition in next year's national elections. The reason: The far right is siphoning off voters who might otherwise support the conservatives, while the left is proving more successful in building ruling coalitions.

``At this point, the political extremes are strengthening each other by giving each other targets to attack,'' says Arnulf Baring, a historian at West Berlin's Free University.

Last Sunday's local voting in Frankfurt and the surrounding state of Hesse underscores the difficulties now facing conservative Christian Democrats. The party - still reeling from heavy losses in West Berlin's January election - suffered another setback, while radical groups gained ground.

Ironically, the conservatives had sought to draw the line in Frankfurt, by picking up on the anti-immigration theme exploited by the far-right to attract voters in the West Berlin election. But on Sunday, the move backfired. Many centrist voters were put off by the tactics. Meanwhile, the tiny neo-Nazi National Democratic Party snared over 6 percent of the vote in Frankfurt, while the far-right Republicans took up to 5 percent in some other districts.

The left-wing Greens pulled in over 9 percent in Frankfurt and have announced their willingness to form a coalition with the left-of-center Social Democrats.

The vote comes at a crucial time. The popularity of the Kohl government has slumped in recent months - fueled by voter reaction against cutbacks in social benefits, the influx of foreigners, and rising taxes. Polls show that the Greens and Social Democrats together draw enough support to outflank the ruling conservatives in national elections.

Indeed, the Greens have long held the potential to tip elections. West Germany allots parliamentary seats to any party that gains 5 percent of the vote, so small parties can play a swing role by backing a larger faction.

Up until now, however, the Green's philosophy - a mix of environmentalism and radical politics - blocked them from forming lasting coalitions on the left. But that's changing.

In West Berlin, the radical Alternative List - that city's version of the Greens - is forming a coalition government with the left-of-center Social Democrats. This follows weeks of negotiations, at the start of which the city's Social Democratic leader, Walter Momper, said he didn't think the Alternative List was capable of forming an effective government.

Analysts will now watch West Berlin - and possibly Frankfurt - to see if leftist coalitions can succeed. If they do, then chances of a national coalition increase.

The Greens are eager to make it work. At a party conference earlier this month, the Greens edged out a faction known as the ``fundamentalists,'' who had long fought against forming coalitions with the Social Democrats.

Meanwhile, the West Berlin coalition faces serious problems. Nearly 60 percent of West Berliners say they'd rather see a new election. Conservatives say they're worried that the city could degenerate into chaos.

Indeed, some political analysts believe the conservatives may be eager to see the leftist experiment fail - since it would fuel their argument that such governments create instability. West Berlin's Social Democrats did talk to the Christian Democrats about forming a ``grand coalition,'' but those talks broke down. Some West German analysts contend West Berlin's Christian Democrats were ordered to pull back by the Bonn leadership - in order to create an ``example'' in West Berlin that could be used in next year's national campaign.

The Alternative List has vowed to work against the presence of the Western allies in the city. Technically, West Berlin is still administered by the United States, France, and Britain, as victors in World War II. The radicals also want to limit the ability of the West German government to exert influence over the city. Because of its special status, all federal laws must be approved by the West Berlin parliament before they can take effect there.

The Social Democrats, who favor more moderate proposals along the same lines, insist that they've gotten assurances that the radicals won't block administration of the city or the enforcement of law and order.