In his most optimistic estimate to date, Senate Majority Leader Robert C. Byrd (D-W.Va.) said yesterday that supporters of the natural gas pricing deregulationl compromise are "virtually over the top" in their search for Senate votes to pass the measure.

If Byrd's count holds, it would represent a major victory for President Carter, who in the past month has waged one of the administration's most intensive lobbying campaigns over the natural gas issuew.

Byrd credited that campign with helping to turn the corner on the compromise. "I think the administration's effort has really been superb," he said. "The administration has probably done its best work" on Capitol Hill in support of the compromise.

The White House's continuing round of briefings for business leaders and other special interest groups on the bill has been particularly effective, Byrd said.

The majority leader avoided making a numerical prediction of the support. There are at least 49 senators now who plan to vote with the administration, he said, calling that estimate "conservative."

That will probably increase, he speculated, after when he predicted would be an unsuccessful attempt to return the compromise to conference committee where it would probably die.

There are 37 senators "hard against it" and 14 "question marks" as the Tuesday voting approaches, Byrd said.

He indicated concern about the "quiet" efforts of some snators to defeat the bill. While he would not name them, he was thought to be referring to Sen. Russell B. Long (D-La.), chairman of the Finance Committee, among others.

The compromise, worked out over 17 months, would deregulate natural gas prices by 1985. Consumer prices would rise but gas production would increase, the administration has argued, helping to relieve the country's reliance on foreign oil imports.

In late August,the 8 prospects of passage were so uncertain that the president cut short a western vacation to return to Washington and begin and all-out lobbying effort.

Carter has been tied up at the Camp David summit for 12 critical days as the Senate wrestled with the measure. Byrd said Vice President Mondale had been particularly effective in Carter's absence although "President Carter has made some calls" to senators during the Middle East Summit.