After months of debate, the Senate Energy Committee appears ready to approve a complex natural gas decontrol bill this week that some observers believe would result in even higher home heating bills than the version originally proposed by the Reagan administration.

But opponents appear ready to resist at length, even filibuster, on the Senate floor, and in the House natural gas legislation seems certain to remain bogged down in committee at least for the rest of the summer if not beyond.

Deregulation battles are always titanic in Congress. The stakes are high, and there are many competing regional and other interests, ranging from those of producers to pipeline companies to utilities like Washington Gas Light and ultimately users. It took Congress 75 bitter weeks to write the last gas bill, the Natural Gas Policy Act of 1978.

That 1978 act established a complex structure of price regulation that would lead to deregulation of all higher-priced new gas by 1985, but would retain price controls on lower-cost old gas, which currently accounts for about half the supply in interstate commerce.

The Reagan administration, however, has been eager to remove controls from all gas, and last winter's aberration of sharply rising natural gas prices at a time when low-cost gas was going begging seemed to provide a golden opportunity to push through new gas legislation.

"But after the real good start that was made, I would say the odds are moving to less than 50-50 of getting something done this year," said George H. Lawrence, president of the American Gas Association, which supports the legislation.

The reason is that for all the thorny side issues, some of which have already tied Senate and House committee members down for weeks, Congress appears about evenly split over the crucial question of whether old gas--that discovered before 1977--should ever be deregulated.

Opponents of deregulating old gas--which currently is being sold to interstate pipelines at an average price of $1.50 per thousand cubic feet--charge that decontrol would produce a $40 billion windfall mostly for the major oil companies at the expense of consumers.

The administration, on the other hand, argues that a free market for all gas would provide the best guarantee of low gas prices over the long haul.

"I think there now is general recognition in Congress that deregulation of natural gas by a date certain is an idea whose time has come," said Robert C. Odle Jr., assistant energy secretary for congressional affairs.

While the administration's bill would lift all controls by Jan. 1, 1986, the bill that seems likely to squeak out of the Senate Energy Committee this week would phase out controls on old gas by raising its price to "market level" in monthly increments over three years.

The legislation also would attempt to bring the price of the highest-cost gas--which accounts for about 5 percent of the current supply--down to market level during the first year after the bill's enactment.

The Citizen-Labor Energy Coalition, which closely tracks gas legislation and has drafted an alternative bill sponsored by 15 senators and 135 House members, calculates that the current Senate formula likely would bring producers an additional $2.5 billion for old gas in the first year while saving consumers $1.2 billion on high-priced gas.

"So prices would go up by at least $1.3 billion just through these provisions alone," said Edwin Rothschild of the coalition.

Beyond that, supporters and opponents of decontrol agree that the version of the bill likely to emerge from the Senate committee will be weaker than the administration's proposal in holding down gas prices during the transition to total decontrol.

"We do not feel the consumer protections are as strong as they were in our bill," said Odle. He cited provisions giving pipelines an incentive to bargain for lower prices by limiting the increases that could be passed on to consumers.

"But our position is: let's move the Senate bill to the floor and not amend it any longer," said Odle. "If the Senate can pass a bill quickly, then that does create a climate for faster action in the House."

The likelihood of early Senate action, however, does not appear high.

Sen. Howard M. Metzenbaum (D-Ohio) said that even if Chairman James A. McClure (R-Idaho) is able to get a bill out of his Energy Committee this week--"and I think it's still touch and go whether he can get it out with decontrol of old gas in it"--it still faces an uphill battle on the Senate floor.

Metzenbaum also repeated his vow to fight any effort to lift controls from old gas "with every weapon in my command, and that includes a filibuster if necessary. There is no stone I would leave unturned."

On the House side, meanwhile, prospects that the subcommittee on fossil and synthetic fuels will finish work on a natural gas bill before the August recess appear to be fading. Even if it does, the full Energy Committee--chaired by John D. Dingell (D-Mich.), who opposes decontrol of old gas--is thought likely to keep the bill bottled up for months.

If a legislative stalemate occurs, some observers think that, when cold weather arrives, concern about a sharp new rise in gas prices--forecast at anywhere from 5 to 16 percent this winter following the 45 percent jump of the past two years--could lead to renewed sentiment in Congress for a "quick fix" such as a price freeze or rollback.

"If we don't do something comprehensive, I think that is a distinct possibility because the people back home will be saying: 'Do something,' " Odle said.

Lawrence of the gas association agreed that the impetus for some type of legislation should grow as fall turns into winter.

"Natural gas legislation is a little bit like Social Security legislation," Lawrence said. "I think many in Congress don't like to fool with it--it's tough and explosive politically--but they're a little fearful not to."

"At the same time, they want a constructive solution they've participated in," Lawrence said. "And if it looks like the comprehensive approach is bogged down, I think they will try to seek a simpler solution."