Despite the loss Friday of one of its most important supporters, the natural gas compromise bill before Congress can still be saved, two powerful senators said yesterday.

Senate Majority Leader Robert C. Byrd (D-W.Va.) said he's not giving up on the compromise "until it is absolutely and obviously and indubitably impossible to think about getting a bill."

And Sen. Henry M. Jackson (D-Wash.), chief Senate negotiator for the compromise, noted that politicking on the bill was "almost like negotiating with the Russians," but said he still believed agreement could be reached.

"We've got a hard, tough week ahead of us," Jack said, "but it's doable."

The measure of optimism of Byrd and Jackson was particularly significant because it came just a day after Sen. J. Bennett Johnston (D-La.), one of the architects of the compromise, announced he would not support the bill as it is written.

Johnston charged that the present draft of the bill differs "substantially" from the concept agreed to in May.

Johnston's colleague, Sen. Russell B. Long (D-La.), said in a radio broadcast Friday night that he believed the compromise would fail unless it were rewritten.

Jackson and Byrd said they do not underestimate the problems facing the natural gas bill, but that they believe the differences can be bridged.

"The important thing is for people not to put the keys in their briefcases . . . put their cloaks on and go home," Byrd told reporters at his weekly news briefing.

"The bill is still alive," he added. "It would be absolutely ridiculous, after 14 months of working, not to produce a bill."

The immediate problem facing supporters of the natural gas compromise is getting a majority of both the House and Senate conferees to sign the bill. Last May, House conferees passed the bill 13 to 12, while Senate conferees approved the measure 10 to 7.

The bill cannot be called up for a final vote unless a majority of conferees from each chamber signs the report.

Staff members spent two months writing the 170-page compromise bill, but some conferees who originally approved it have wavered on signing the current draft.

"The key will depend on the need to have some clarification of the language which is in the conference report," Jackson said yesterday. "I don't think that problem is irreconcilable."

Overall "The margin as far as approving the conference report is too close to call," Jackson said.

If the bill reaches the Senate floor, Jackson said, supporters can fend off a filibuster promised by opponents Sen. James Abourezk (D-S.D) and Sen. Howard M. Metzenbaum (D-Ohio).

Should the compromise bill fail, the issue of natural gas deregulation would not come up again in Congress for several years. Jackson added.

"We are either going to do it in this Congress, or it is dead. We will not have this problem again," he said.

Jackson also noted that failure of the compromise could have serious effects on the proposed natural gas pipeline from Alaska across Canada and into the Midwest.

The compromise bill would allow the higher transportation costs of gas coming through this pipline to be averaged in with the transportation costs of cheaper gas from the Gulf Coast states.

"If this compromise fails, the Alaska pipeline is in deep trouble," Jackson said.