Interior Secretary James G. Watt moved yesterday to resolve one of the most divisive issues of his two stormy years in office, saying he will never again allow oil and gas leasing in wilderness areas.

Watt, in remarks that surprised environmentalists and left them still suspicious, also said he would ban oil and gas leasing on wild lands and forests now under study for possible inclusion in the federal wilderness system--an estimated 27 million acres, in addition to the 80 million wilderness acres already designated by Congress.

Perhaps the most fundamental dispute between Watt and environmentalists has been over his desire to increase energy and mineral exploration on public lands, particularly along coastlines and in wild areas.

Just five days ago Watt further fueled this dispute by announcing plans to drop 805,000 acres of wild western lands from consideration for possible designation as wilderness. And he stressed yesterday that the new leasing ban does not extend to these acres.

But his statement apparently does mean that the government will never again authorize oil and gas leasing in wilderness areas without special congressional approval, since federal law prohibits granting leases or mineral rights in the wilderness after Dec. 31, 1983.

"This disposes of the issue for us as a practical matter, and we're relieved," Watt said in a briefing for reporters, during which he unveiled an annual report on his department entitled "A Year of Progress."

"I gave my best shot at it," Watt said. "Congress' wisdom will prevail."

He noted that Congress, as a rider to Interior's fiscal 1983 appropriations bill which President Reagan has signed into law, voted to forbid wilderness leasing anyway until next Oct. 1, leaving only a three-month "window of opportunity" until Dec. 31 when the permanent prohibition already in the law takes hold.

But he vowed not to "slip things through" in this window. "That would be inappropriate, in my judgment," Watt said.

Watt drew no praise from environmentalists. Some said they do not trust his verbal promises and cited his action on the 805,000 acres as evidence that he is "hostile to wilderness."

Two environmental groups have announced plans to file suit in an attempt to protect the acres, saying that up to 5.9 million acres could eventually be eliminated from consideration for the wilderness system under the same legal ruling that authorized the department to drop the first 805,000.

"One feels a little dubious about congratulating a secretary for saying he's not going to do what Congress has said should not be done," said William A. Turnage, executive director of the Wilderness Society. "It's a little like congratulating someone for not beating his spouse."

"He has a history of misleading people about his intentions," said John McComb, director of the Sierra Club's Washington office. "If he really means it and his successors abide by it, it would be a step in the right direction. But we have to wonder whether he's just saying this to stop Congress from legislating a ban."

Watt declined to say whether he would support a legislative proposal to impose an immediate ban on wilderness development. The measure, opposed by the Reagan administration, passed the House this year by a lopsided vote of 340 to 58, and was co-sponsored by 54 senators. It died in the Senate Energy and Natural Resources Committee, but is expected to resurface in the new Congress.

Rep. John F. Seiberling (D-Ohio), a leading congressional advocate of wilderness and a sponsor of the measure, had this comment on Watt's remarks: "I must say it's kind of gratifying to know that at least he's cooperating to some extent."

Meanwhile, Interior's decision to eliminate wilderness protections on the 805,000 acres of western lands came into question yesterday.

Watt cited as the basis of the decision a ruling by Solicitor William H. Coldiron saying the Carter administration invoked the wrong section of a federal law to designate areas under 5,000 acres as potential wilderness lands. Under that section, small areas do not qualify for wilderness consideration, Watt said.

However, 1979 Interior documents show that the department did not use the section cited in Coldiron's ruling, but rather another section that allows consideration of smaller areas. The mistake occurred a year later when the agency published lists of the areas being studied in the Federal Register, and cited the wrong section of federal law in explaining the policy.

Watt said yesterday that Interior officials in Utah corrected the error with a register notice several months ago. As a result, he said, Interior will not drop wilderness protections from 14 wild areas covering 25,187 acres in that state, as originally announced. He also said the department will consider reinstating protections on the 3,520-acre Bisti Badlands in New Mexico, a prized natural area that was eliminated by this week's ruling.

Watt's comments yesterday marked a further evolution of his policies on wilderness, defined by Congress as areas "where the earth and its community of life are untrammeled by man." The federal wilderness act bans development and motorized traffic in those areas.

After Watt's initial stand on wilderness leasing drew angry bipartisan resistance, Watt agreed to a leasing moratorium until at least the end of the 97th Congress. He invited lawmakers to use the time to set a national policy.

He then proposed legislation to impose an immediate ban on wilderness mining and drilling, but only for 18 years--a measure denounced by environmentalists as a "wilderness destruction bill."