WASHINGTON - Top Democrats in the Senate have reached an agreement to extend the soon-to-expire $8,000 tax credit for first-time homebuyers, Senate Banking Committee Chairman Christopher Dodd said on Tuesday.

We have that. Done, Dodd told reporters. He declined to specify the details of the agreement.

But a Republican who has worked with Dodd cautioned that they were still negotiating on the measure, which could come up for a vote on Tuesday evening as part of a package that would extend unemployment benefits.

We're close, we're close but I can't get into any details until it's a done deal, said Republican Senator Johnny Isakson.

The popular tax credit, which has helped lift the housing market out of its worst slump since the Great Depression, is set to expire on November 30.

Dodd and Isakson want to extend the credit through June of next year and broaden it to anyone buying a primary residence, not just first-time buyers.

Senate Majority Leader Harry Reid had backed a narrower version which would extend the full credit through March and gradually phase it out through the end of 2010.

Dodd said that the deal would merge the two proposals.

(Reporting by Corbett B. Daly and Andy Sullivan; editing by Sandra Maler)