Many election years are predictable, as the parties play to their bases and legislative gridlock usually strikes Capitol Hill.

But the first five weeks of this year have brought some surprises. House leaders of both parties and the Bush administration ironed out a deal on an economic stimulus bill. Leading presidential candidates criticized the legislation, but it easily passed the House, 385-35.

It was widely expected that the legislation would sail through the Senate, but members of the upper chamber, most notably Senate Finance Committee leaders Max Baucus (D-Mont.) and Chuck Grassley (R-Iowa), significantly expanded its scope.

That has put the White House and other leading Republicans in the unusual position of calling for the speedy passage of the House bill, with its smaller tax rebate cap of $75,000 for individuals and $150,000 for couples. The Baucus-Grassley bill would double those caps while adding business tax breaks and an extension of unemployment insurance.

The White House and Senate Minority Leader Mitch McConnell (R-Ky.) are making the case for speed instead of larger tax rebates, claiming that the economy needs a boost as soon as possible.

Baucus predicted this week that he has the necessary 60 votes to clear his bill through the Senate floor. But the vote Wednesday is expected to be close. At first, Senate Majority Leader Harry Reid (D-Nev.) had said the vote would come two days ago, forcing Sens. Hillary Rodham Clinton (D-N.Y.), Barack Obama (D-Ill.) and John McCain (R-Ariz.) to make a difficult choice about whether to return to the Capitol the day before Super Tuesday. Reid subsequently moved the vote to Wednesday.

Reid favors Baucus’s package, though he initially said the Finance chairman’s decision to totally remove the House-income caps on tax rebates made him want to “gag.” Baucus did put caps back in, though much higher than the House’s.

As the bill works its way through the Senate, bipartisanship on the stimulus package seems to be fraying. Angered by McConnell’s statements that Republicans had little opportunity to read the Senate bill, Reid Monday called the minority leader’s comment “shallow.”

He quickly backtracked, apologized for going too far and struck his “shallow” remark from the record.

Still, more battles on the stimulus appear to be inevitable because even if the Senate passes its bill, it will take time to hash out the final legislation with the House. All indications are that a measure will be sent to President Bush’s desk by the end of next week. But based on the rare bipartisanship that has emerged in the partisan-charged House, and the fact that Democrats are pushing for larger tax rebates for higher-income taxpayers, predicting the end game on this stimulus package is tricky business.