Interior Secretary James G. Watt yesterday attempted to prevent a split with key congressional Republicans by offering to compromise on his controversial wilderness bill, which has drawn opposition from across the political spectrum.

But Watt's offer, contained in a draft of testimony, was quickly discounted as a "public relations gimmick" by Rep. John F. Seiberling (D-Ohio), chairman of the House subcommittee on public lands and national parks that is to hold hearings on the bill Monday.

"Secretary Watt is fond of saying that the word 'compromise' is not in his vocabulary," Seiberling said. "He has made so many disingenuous statements on this issue that you have to wonder how serious he is. I find it very difficult to take anything about this bill seriously."

"To consider the proposals of this legislation 'set in concrete' . . .would be inaccurate," the testimony says. However, the rest of the 15-page draft defends each feature of Watt's wilderness proposal, a bill Seiberling denounced as an attempt to "gut the nation's wilderness system." Influential Republicans on the subcommittee also denounced it.

Interior officials said Watt is willing to call for a ban on mining and drilling in wilderness beyond the year 2000, the cutoff date he proposed in his original measure. They said, however, that Watt would refuse to compromise on his proposal to impose a deadline after which Congress can no longer place lands under wilderness protection. Subcommittee Democrats find that proposal one of the most objectionable.

Rep. Richard Cheney (R-Wyo.) and Rep. Manuel Lujan (R-N.M.), both cosponsors of the measure, have recently urged Watt to change certain features of the bill--for example, the proposal to open wilderness areas to development after the year 2000.

The pressure from Cheney and Lujan, both conservative Republicans who often side with Watt, is viewed as a sign of growing public opposition to Watt's wilderness policies, even in western states where his pro-development policies often receive warm support.

Cheney said he had received more than 1,000 letters of protest over reports of possible oil and gas development in his state's Washakie wilderness area, "and these include a lot of folks who are oftentimes frustrated with the federal government."

"I'm not just talking about environmentalists," Cheney said yesterday. "I'm talking about ranchers, farmers, snowmobile advocates, hunting and fishing guys as well as a lot of folks in the oil patch who are eager to develop resources but who believe a certain part of the state ought to be off limits."

A key House Republican who asked for anonymity, said he and others had told Watt that "it's a political loser for him to proceed with the bill as it is. Republicans would have to choose between supporting Secretary Watt and the administration, or supporting their constituents."

Watt's measure, which he portrays as a wilderness protection act, would ban mining and drilling on 24 million acres of pristine wilderness in the lower 48 states until the year 2000. Initially viewed as a major compromise, it has since been attacked for having what Seiberling calls "a loophole as big as the whole wilderness system."

Watt's proposal would empower the president to open certain wilderness areas for mineral development in cases of "urgent national need" without congressional approval. Under present law, those lands would be open to leasing only until 1984 and would then be protected indefinitely. Present law also prevents the president from opening wilderness lands without a vote of Congress.

In his draft testimony, Watt repeated his contention that he supports "protecting our wilderness lands for the enjoyment of all Americans now and in the future," and keeping them as "the last to be explored or developed."