WASHINGTON  The Senate Republican leader proposed legislation on Monday to continue all of the Bush-era tax cuts indefinitely, testing the willingness of Democrats to allow a tax increase on the wealthiest Americans in a weak economy and making clear that a partisan fight will extend deep into the campaign season if not beyond.

The proposal by the Senate leader, Mitch McConnell of Kentucky, came a day after the House Republican leader, John A. Boehner of Ohio, suggested a potential compromise, saying he would vote for President Obama’s plan to extend the cuts only for households earning less than $250,000 if he had no other choice.

In part, Mr. McConnell’s proposal illustrated the greater leverage that Republicans enjoy in the Senate, where they control 41 seats  enough to filibuster and block any bill. While Mr. Boehner cannot stop House Democrats from forcing a vote on the president’s favored tax plan, Mr. McConnell made clear that he would have a say and that he wanted to put a handful of wavering Senate Democrats on the spot.

But Mr. McConnell’s position also served as a political counterweight to Mr. Boehner’s statement on Sunday, which suggested that some Republicans wanted to avoid a brawl in which they would be cast as blocking tax relief for the middle class to ensure that tax cuts continued for the wealthy. Senate Republicans, by contrast, seem to relish the fight.