Negotiations have begun in earnest on another short-term extension of aviation programs and taxing authority for the Federal Aviation Administration which the Senate could pass this week.

The FAA's current short-term extension (PL 110-190) expires June 30. Senate Democrats are seeking quick consideration of another extension by unanimous consent, according to Steven Broderick, a spokesman for John D. Rockefeller IV, D-W.Va.

Lawmakers had hoped to pass a four-year reauthorization bill (S 1300, HR 2881) before June 30 but abandoned that plan when the Senate became bogged down in disputes over both process and substance.

Democrats will probably strip out the text of a previous short-term extension that was not acted on in the Senate (HR 3540) and use it as the vehicle for the next extension.

It "should happen this week, but tough to say when," said Stephen Krupin, a spokesman for Majority Leader Harry Reid, D-Nev.

A Senate Republican aide said Republicans generally would prefer a longer extension through next year and may also press for quick action by unanimous consent of a Republican alternative along those lines.

Lawmakers have gone back and forth over how long the extension should be. Members of the Finance Committee generally prefer a shorter extension, and those on the Commerce, Science and Transportation Committee generally want one that would last through next year.

Senate Democrats seem to have settled on a shorter time frame -- on Monday they were floating a proposal that would run through the end of September.

However, there is some concern that Republicans may object to a portion of the proposal that would allocate $8 billion from the Treasury to shore up the Highway Trust Fund, which faces a significant shortfall in fiscal 2009 without an infusion of cash.

A Senate aide said the $8 billion would not be offset. Similar language was included in the four-year bill, but the money was offset with revenue-raisers that Republicans disliked. Disagreements over those offsets, which included items such as pushing back the taxable date on offshore tax haven companies, helped tank the measure on the floor, necessitating another extension.

The $8 billion being discussed for the new extension would be a direct appropriation from the Treasury into the trust fund. Democrats have begun preparing a counterproposal in case Republicans object to the non-offset $8 billion in highway funding.

Jim Berard, spokesman for the House Transportation and Infrastructure Committee, said that a four-year bill would be preferable but that another extension through the end of the fiscal year signals there may be hope to complete the bill before year's end.

"September 30 is a reasonable extension but it also is anticipating that we could get [through conference] by then," Berard said. "For now we're just going to see what we can do."