Hans-Dietrich Genscher, brushing aside demands that he step down as chairman of the strife-torn Free Democratic Party, declared tonight he would run again for the top party post at a national congress in Berlin Nov. 5.

His announcement threatened to widen the rift in the small centrist party, which has been bitterly divided over the way Genscher, who is also the Bonn foreign minister, rapidly switched his party from a long-time alliance with Social Democrat Helmut Schmidt into a new coalition with conservative Helmut Kohl two weeks ago.

As an apparent gesture to Genscher's critics, it was announced that Uwe Ronneburger, a respected moderate deputy from Schleswig-Holstein, has also decided to run for the chairmanship.

The news came after a five-hour meeting of the Free Democrats' 10-member presidium, which was reported deeply split over Genscher's candidacy.

Demands for his removal have come from Free Democratic moderates such as Hildegard Hamm-Bruecher, formerly minister of state under Genscher in the Foreign Ministry, as well as left-wing party members such as Gerhart Baum, who served as interior minister in the previous government.

The moderates regard Genscher as a liability now in new national elections promised for next March. Since the breakup of the old coalition, he has become the least popular major politician in West Germany. The party's left wing objects to him for maneuvering the Free Democrats into partnership with the Christian Democrats.

Both factions are incensed over what they see as Genscher's secretive scheming for the change in coalition partners. They argue that his continued presence as chairman would inhibit reunification of the party.

Regional party branches in Bavaria and Baden-Wuerttemberg have lately joined the chorus of those insisting on a new chairman. And leftist Free Democratic parliamentarians have hinted that if Genscher does run again, they may break off and try to form a new party or align themselves with the Social Democrats.

But Genscher, who has chaired the party for eight years, was determined to stand again, gambling on the likelihood that he still has a grass roots majority.

Explaining his decision in a television interview tonight, Genscher said it was necessary that he run in order to defend and confirm his decision to lead the party into a new coalition. He called Ronneburger's rival candidacy "correct," because it would offer his critics an alternative. But he said that Ronneburger and all other members of the presidium had agreed not to demand at the convention that the new partnership with the Christian Democrats be cancelled.

Two crushing Free Democratic defeats in regional elections in Bavaria and Hesse since the breakup of the old Bonn government have contributed to the erosion of Genscher's support at all party levels.

Meantime, amid continued doubts about whether national elections will actually be held in March as pledged by Kohl and Genscher, the government was said today to be studying a report by Interior Minister Friedrich Zimmermann outlining several options that would pave the way for the dissolution of parliament.

None, however, is clearcut. The West German constitution has no provision for the chancellor or parliament to call for new elections when there exists, as now, a political majority capable of governing.