Late this week, budget talks between the Bush administration and Congress should evolve from preliminary, technical discussions into hard bargaining with election-year politics and billions of dollars at stake. But none of the participants pretends to know what will happen. ``I wouldn't hazard a guess,'' said one, Senate Budget Committee Chairman James Sasser, D-Tenn. ``These things can go on for so long, and then suddenly as if by magic you seem to reach a critical mass and then there's an agreement.'' After five weeks and eight private sessions, the Democratic and Republican sides agree that somewhere between $45 billion and $60 billion in new taxes and spending cuts are needed for fiscal 1991, which starts Oct. 1. Unless some deal is worked out by that date, the Gramm-Rudman deficit-reduction law will force tens of billions of dollars worth of spending cuts, an amount both parties say is intolerable. Yet neither side is eager to be the first to lay a plan on the bargaining table at sessions continuing this week, and risk being accused of championing something that the voters might find dreadful. Among the battlegrounds: will Democrats have to swallow cuts in some of their favorite social programs? And will President Bush's campaign mantra of ``No new taxes'' become obsolete? Democrats say the bargaining can only begin with a concrete offer from Bush, who called for the talks early last month. ``I thought implicitly at the beginning that the administration would present a proposal here,'' Sasser said last week. But Republicans say there is no need for the White House to lay down a proposal, and it has no plans to do so. If Democrats continue to insist that Bush present a budget proposal, ``It would be clear at that point that the Democrats don't intend to work out an agreement,'' said a GOP bargainer, Sen. Phil Gramm of Texas. Rep. Bill Frenzel of Minnesota, a Republican negotiator who will retire from Congress this winter, said he might be willing to push a plan forward if no one else will. ``If they need a fall guy, and it's said that lame ducks are good at that kind of stuff, I wouldn't mind being put in that position,'' he said. But that's not likely to satisfy Democrats. ``We're not interested in hearing from Republican legislative members,'' said Sasser. ``That's not what it's all about. This is a negotiation between the executive and legislative branches.'' Contributing to the unpredictability of the talks is the schizophrenic outlooks of the Democratic and Republican teams. Each side has pragmatists like White House budget director Richard Darman and House Budget Committee Chairman Leon Panetta, D-Calif. They seem above all to want a deal that once and for all takes a bite out of the federal deficit, which some project could exceed $200 billion next year. But the two teams also have highly partisan members, such as Sasser and White House chief of staff John Sununu, who seem leery of agreeing to anything that might provide a campaign advantage to the other party. Bargainers say the litmus test for the talks will be whether they have accomplished anything by the start of Congress' July 4 recess. They argue that agreement is needed by around then for lawmakers to have time this year to enact a deficit-reduction package. ``Everyone feels that if we work day to day until then, we ought to be either well on our way to putting an agreement together or be pretty much facing a task that's harder than everybody thought,'' said Panetta.