WASHINGTON — Lawmakers are trying to extend and expand an $8,000 federal tax credit for first-time homebuyers, a stimulus-package tax break that many regard as a significant prop for the still-tottering economy.

The latest Senate proposal would drop the requirement that the credit be available only to first-time buyers, broadening the reach of the program but also adding to its cost, estimated by congressional analysts at $16.7 billion.

The backers of that idea, Sens. Johnny Isakson, R-Ga., and Christopher Dodd, D-Conn., chairman of the Senate's banking committee, have suggested that their measure be attached to another pending bill aimed at throwing a lifeline to people hit by the recession, an extension of federal assistance to the millions in danger of exhausting unemployment insurance benefits.

Extending the homebuyers' credit and unemployment benefits are among several primary means being pushed by the administration and Congress to help people get through the prolonged economic downturn.