The Federal Energy Regulatory Commission -- Poised a few weeks ago to relax controls on natural gas prices--has delayed action and is proceeding more gingerly in the face of strong public and congressional protest.

Since March 10--the date originally set for a vote on whether to issue a proposed rule that would have lifted the average price of natural gas--action has been postponed twice. In addition, the proposal has been softened and converted into a more preliminary step toward what critics have called "backdoor deregulation."

"In part, it's a response to a lot of concern over the possibility of adjusting the prices on old gas," said Rachelle Patterson, director of public information for the FERC. Patterson said the commission meant to emphasize the fact-finding nature of its activities.

The FERC's recently appointed chairman, C.M. (Mike) Butler III, had advanced the notion that prices of all "old" gas--gas found before 1977, which accounts for more than half the gas in the system--should be raised to the highest allowable price for any of that gas. To do so would be to raise the average gas price at the consumer level by more than 30 percent, or about $10 billion, in the next year.

The proposal was floated before President Reagan announced March 1 that he would not introduce legislation to accelerate natural gas decontrol this year. Commissioners then were less timid about talking about "administrative decontrol".

Whether the delay is only temporary remains to be seen, but it appears that not all the commissioners are ready to follow Butler's lead. "The whole thing may just evaporate" because of changing market conditions, said Commissioner Georgiana H. Sheldon. Testifying before the Senate Energy Committee yesterday, Butler said he had not proposed any immediate decontrol but said the agency has the power to authorize higher prices if they are "just and reasonable."

Even if the commission acts, the administrative process and court challenges could delay any change until the issue is moot, Sheldon said earlier. "I would be one who would go very cautiously," she added. "When you're talking about billions and billions of dollars, you should be sure of your facts."

The notion that the FERC might do what Congress was reluctant to do produced an immediate outcry. On Capitol Hill, House and Senate Democrats attacked "back-door" decontrol, and groups that were set to lobby against a legislative attack on natural gas price controls turned their attention to the FERC. A bipartisan group of 29 senators yesterday spoke out against any immediate natural gas price boost.