WASHINGTON — Republican lawmakers, scrambling to reach agreement on a final tax bill that they hope to pass next week, are coalescing around a plan that would slightly raise the proposed corporate tax rate, lower the top rate on the richest Americans and scale back the existing mortgage interest deduction.

In a frenzy of last-minute negotiations, Republicans drew closer to agreement on nudging the corporate tax rate to 21 percent, up from the 20 percent in the bills that passed the House and Senate but still lower than the current 35 percent corporate rate, according to a lawmaker and a person briefed on the discussions.

They are also considering lowering the top individual tax rate to 37 percent, from the current top rate of 39.6 percent, to assuage concerns from some wealthy taxpayers who fear that their tax bills could rise under the current legislation, which eliminates a host of individual tax breaks.

Another closely watched change centers on the ability to deduct the interest on mortgage debt. Lawmakers are discussing limiting the deduction to mortgage debt of up to $750,000 for newly purchased homes, a higher cap than the $500,000 limit in the House-passed bill but lower than the $1 million limit that currently exists and remains in the Senate-passed bill, according to Senator John Kennedy, Republican of Louisiana.