WASHINGTON — Top Republicans on a key Senate panel have reached a tentative agreement on a tax plan that would add about $1.5 trillion to the government’s $20 trillion debt over 10 years, according to congressional officials.

Tennessee Sen. Bob Corker, a member of the chamber’s dwindling band of deficit hawks, said on Tuesday that Republicans have “potentially gotten to a very good place” on agreeing to how much the upcoming tax measure might cost, once the Senate’s tax writers have blended together rate cuts, additional revenue raised through curbing tax breaks, and the beneficial effects of what he called “pro-growth tax reform.”

“We’ll have something for you a little bit later today,” said Sen. Pat Toomey, R-Pa., a participant in the negotiations from the party’s more aggressive side on tax cuts.

Corker didn’t offer a number, but officials familiar with the Senate Budget panel’s internal discussions said the allowance for the tax measure would amount to $1.5 trillion.

The figure would allow deeper cuts to tax rates than would be allowed if Republicans followed through on earlier promises that their upcoming tax overhaul wouldn’t add to the deficit. That would represent an about-face for top Capitol Hill Republicans such as Senate Majority Leader Mitch McConnell and House Speaker Paul Ryan.