WASHINGTON – The Senate thwarted efforts Wednesday to block Bush administration pollution rules and to double aid for drought-stricken farmers as Republicans batted down Democratic amendments to a sweeping $390 billion spending bill.

By 50-46, the GOP-controlled chamber killed an effort by Sen. John Edwards, D-N.C., to delay Environmental Protection Agency regulations that will let factories, refineries and processing plants modernize without upgrading their air pollution systems.

Maine’s Sens. Olympia Snowe and Susan Collins were among a few Republicans to break away from their party and vote for the amendment, to the applause of environmental groups in their home state.

Both senators have been critical of Bush’s air pollution policy, a common stance among New England politicians because of northeasterly wind currents. Increased industrial pollution in the Midwest likely would result in reduced air quality in Maine.

The Senate vote was a victory for President Bush in the first major environmental showdown of the new Congress and briefly shined the spotlight on Edwards, a 2004 presidential hopeful. It was hailed by industry groups as a boon to business and criticized by environmentalists who said it would result in dirtier air.

“What are we going to say to … the kids who have had asthma attacks, the seniors who have had serious heart and respiratory problems” if the rules take effect, Edwards said.

Opponents said the rules will let plants that are expanding or being repaired improve their air-quality controls without being forced by the government to use the most expensive state-of-the-art equipment.

“The Senate has chosen cleaner air and energy efficiency over Democratic presidential politics,” said Frank Maisano, spokesman for a coalition of utilities that worked against Edwards’ amendment.

Later, the Senate by 56-39 turned aside an amendment by Senate Minority Leader Tom Daschle, D-S.D., that would have roughly doubled the $3.1 billion the overall measure has for farmers. Instead, senators voted 59-35 for an alternative by Sen. Thad Cochran, R-Miss., focusing more of the money already in the bill for growers and ranchers hurt by natural disasters.

On the fifth day of debate, both parties’ leaders predicted for the first time that the Senate could complete the long-delayed spending bill by Thursday night.

The measure is an amalgam of 11 bills for the federal fiscal year that started Oct. 1, covering every agency but the Defense Department, whose budget was enacted last fall.

Democrats said they had scored enough political points by spending days trying – mostly unsuccessfully – to add funds for schools, farmers, domestic security and other programs. Republicans have all but abandoned hope of sending a final House-Senate bill to Bush in time for his State of the Union address Tuesday, but were nonetheless eager to move on to other issues.

“We’re finding very little fiscal responsibility, and very little shame, really, on the other side,” Sen. George Allen, R-Va., said of the parade of Democratic spending amendments that majority Republicans have been defeating since last week.