The Maine House of Representatives gave preliminary approval this afternoon to a bill that would avert a showdown with the federal government over what the U.S. Department of Homeland Security views as Maine's lax procedures for issuing driver's licenses.

The 73-69 vote, which capped a two-hour debate, was inconclusive because the House now is awaiting an amendment that would water down the bill.

Among other things, the bill would force non-citizens to prove that they are in the country legally before they can qualify for a Maine license.

Gov. John Baldacci promised to propose that change and others to the Legislature after Homeland Security threatened to stop accepting Maine driver's licenses as a valid ID for boarding commercial flights and entering federal buildings.

Baldacci's pledge lifted that threat and prompted Homeland Security to give the state a conditional extension for complying with other provisions of the federal Real ID Act, which is designed to make all of the states' driver's licenses more secure.

The extension is conditional because the federal agency is demanding that the state implement the initial round of security measures by this December to retain an extension through late 2009.

Supporters of the proposed changes describe them as reasonable anti-fraud measures that the state must implement to avoid subjecting Mainers to added screening at airports and federal buildings.

Opponents say the federal government is trying to coerce Maine into implementing an unfunded mandate that threatens civil liberties and privacy without improving national security.