WASHINGTON — Senate Democrats said Monday that they would try for the fifth time in two months to raise taxes on top earners to pay for legislation that would reduce Social Security payroll taxes, as President Obama sought to keep Congressional Republicans on the defensive, asserting that their intransigence could cause a tax increase for tens of millions of American workers.

With Republican and Democratic leaders deadlocked over the issue in both chambers, two senators offered a bipartisan compromise that they said could help break the impasse before Congress adjourns for the year.

The proposal, devised by Senators Susan Collins, Republican of Maine, and Claire McCaskill, Democrat of Missouri, would extend the current payroll tax cut for employees and reduce the employer’s share of the payroll tax as well. It would also provide additional money for highways, bridges and other job-creating transportation projects.

It would offset the cost with a 2 percent surtax on income in excess of $1 million a year, but would carve out protection for many small-business owners who report business income on their personal tax returns.