WASHINGTON — House Speaker John Boehner publicly blessed a Republican deficit-reduction plan Tuesday that would raise $300 billion in additional tax revenue while overhauling the IRS code, bucking opposition by some GOP presidential hopefuls and colleagues wary of violating a longstanding point of party orthodoxy.

Boehner, the top Republican in Congress, spoke as time grew perilously short for agreement by the deficit-fighting "supercommittee." The panel has until a week from Wednesday to vote on any compromise, but several officials said that in reality, perhaps as little as 48 or 72 hours are available to the six Republicans and six Democrats.

While Boehner's voice is important, his endorsement does not mean all Republicans will follow him or that a deal is in sight. Republicans have been unified for two decades in opposition to higher taxes, while Democrats on the supercommittee insist on additional revenue before they will agree to cuts in benefit programs like Medicare as part of a compromise.

The speaker said that the plan, outlined a week ago to Democrats on the committee, was "a fair offer." Adding tax reform would generate economic growth, he said, speaking as the supercommittee groped uncertainly for a compromise to reduce red ink by $1.2 trillion or more over a decade.

Any deal must be certified by the nonpartisan Congressional Budget Office as meeting the $1.2 trillion target, circulated to lawmakers and then posted publicly before the committee takes formal action. Failure to act would trigger $1.2 trillion in automatic deficit cuts in 2013 that both sides say they want to avoid.

The full committee hasn't met in several days, but various subgroups have been in near constant contact.

More than deficit reduction is at stake, one year into an era of divided government.