The League of Women Voters said Monday it is withdrawing as sponsor of the presidential debate in Los Angeles later this month, throwing into doubt the second nationally televised confrontation between George Bush and Michael Dukakis.

Spokesman Bill Woodwell said League president Nancy Neuman would explain the decision at a news conference Monday afternoon and refused further comment.The debate was scheduled for Oct. 13 or Oct. 14 in Los Angeles, depending on the baseball playoff schedule.

Democratic National Chairman Paul Kirk, campaigning Monday with Dukakis in Connecticut, said if the League does pull out, a joint party debate commission could assume sponsorship and hold the second debate either as scheduled or after a brief delay.

Sources said the agreement between the two campaigns calls for each side's "best efforts to obtain a mutually agreeable sponsor" if one of the original sponsors drops out.

There was no certainty Bush would agree to a new sponsor. The GOP nominee holds a narrow lead over Dukakis in national public opinion polls and was the one who insisted on League involvement in the debates.

Kirk brushed aside any possibility that Bush might not participate: "They may try, but I don't think they can. They are committed to two presidential debates and the American people are well aware of that."

Bush, at Edwards Air Force Base in California, said he was not aware of the League's withdrawal. When reporters asked Bush whether he would attend if the joint party commission picked up sponsorship, the vice president said, "I can't answer a hypothetical question."

Republican Dan Quayle, meanwhile, believes the vice presidential debate will enable him to dispel doubts harbored by some about his candidacy. Democrat Lloyd Bentsen, still uncomfortable with the format, is relying on mock debates and intense preparation to ready for the encounter Wednesday night in Omaha, Neb.

Quayle, in a pre-debate interview with The Associated Press, said that although the vice presidential encounter is important, the determining factor for American voters is the candidate for the White House - and the Indiana senator will direct his attacks at the Democratic nominee.

"The opponent for me is Michael Dukakis. He's the one that's running for president," Quayle said. "The senator from Texas is the vice presidential nominee, and my target and my discussion and my focus that evening will be on the governor from Massachusetts."

Bentsen, meanwhile, held a mock debate with Quayle stand-in Rep. Dennis Eckart, D-Ohio, and then flew to Austin, Texas, to devote his time to debate preparation.

In the mock session, Eckart's attacks sent staffers scurrying for research material, and left Bentsen a bit uncomfortable with the debate format - 90 minutes of questions, two-minute responses and one-minute rebuttals.