It may be November before the U.S. Congress completes the new $500 billion U.S. farm bill as lawmakers cannot agree on how much to cut support to farmers or food stamps for the poor.

"We're stuck at the moment," said Senate Agriculture chairwoman Debbie Stabenow. "All we need is a bill from the House ... we could negotiate during October and pass it when we get back in November."

It was the gloomiest forecast yet from a farm bill leader and came a day before the Capitol Hill rally to propel the bill to passage before current law expires on Sept 30. The House has been deadlocked since July over larger cuts in farm supports and food stamps for the poor.

The delay comes as about 60 farm and agribusiness groups have scheduled a Wednesday rally on Capital Hill to get a Farm Bill passed.

The Democrat-controlled Senate wants to eliminate almost all traditional farm subsidies and replace them with a system that compensates growers when revenue from a crop is more than 10 percent below average. Crop insurance would cover deep losses.

Lawmakers opened a brief pre-election session on Monday but plan a post-election session in November and December to focus on deficit reduction. The Republican-run House scheduled eight days of work this month and will vote later this week on a stop-gap bill to fund the government until March.

DELAY SHOULD NOT AFFECT FARMERS

There would be little immediate impact on farmers or commodity markets if the 2008 farm law expires. So long as Congress appears on road to passing a farm bill, the Obama administration could refuse to heed an underlying Depression-era law that limits plantings and sets sky-high support prices.

Five dozen farm and agribusiness groups in the Farm Bill Now coalition scheduled a rally at the foot of Capitol Hill on Wednesday with Stabenow as a headline speaker.

House Agriculture Committee chairman Frank Lucas, who declined to speak at the rally, has a goal of passing a new farm bill but says he cannot predict when it will happen. Republican leaders say the Senate bill is unacceptable.

The deadlock in the House allowed Democrats to score election-season points while calling for lawmakers to do their jobs.

"They're only working eight days in September," said Agriculture Secretary Tom Vilsack in a speech to an ethanol trade group. "How about working all the way to Sept 30 to get the job done?"

If there is no agreement on a farm bill in coming weeks, Congress could extend the 2008 law briefly or for a long time. Some lawmakers say a one-year extension is likely. (Reporting By Charles Abbott; Editing by Bob Burgdorfer)