Only one vote and possibly a few federal judgeships - are stopping Senate Democrats from shutting off a Republican filibuster and passing the first increase in the $3.35 hourly minimum wage since 1981.

But having lost two cloture votes last week in trying to break the logjam, Democratic leaders were unwilling to schedule a third attempt until after Sunday night's debate between presidential candidates George Bush and Michael Dukakis.Republican leaders following a White House-directed legislative strategy are insisting on paring down by about half the $1.20 increase in the minimum wage that Democrats would like to implement over a three-year period.

The Republicans also want to couple the increase to a new 90-day, 85 percent subminimum wage for newly hired workers, as long as no one would fall below the current $3.35 floor.

The minimum wage bill is one of several facing an impatient Congress eager to adjourn to hit the fall campaign trail.

Senate Majority Leader Robert C. Byrd, D-W.Va., has warned senators to be prepared for Saturday sessions if the 100th Congress is to end by Oct. 16 - a date two weeks beyond the original target date for finishing business.

Behind the scenes, GOP leaders are holding the minimum wage bill hostage while trying to win a commitment from Democratic leaders to act before Congress adjourns on an unspecified number of the 29 federal judicial nominations that President Reagan has sent to Capitol Hill.

Recalling that 17 of President Carter's judicial nominations disappeared in the interim between the November election in 1980 and Reagan's taking office the following January, Republicans are determined that the same will not happen to them should Dukakis win.

Senate GOP Whip Alan Simpson of Wyoming made it clear that any "deal" for allowing Democrats to move the minimum wage bill and possibly act on other social and environmental legislation does not have to involve all 29 of Reagan's nominees to the bench.

"A shake of the hand will do it - we do not need to have it in writing - that these certain judges will be approved," Simpson said. "That is really the issue before us and it really does not have anything to do with the minimum wage."

Sen. Edward M. Kennedy, D-Mass., the primary sponsor of the minimum wage increase, expressed confidence in picking up the 60th vote needed to end the filibuster, regardless of whether a deal is struck on the judicial nominations.

Last Friday, eight Republicans - five more than on Thursday - joined 48 Democrats in a 56-35 vote seeking to break the filibuster. "I believe we're on the edge of having a successful resolution," Kennedy said.

GOP leaders, however, were confident that no more members in their party would break ranks and suggested that a few might even switch back.