A monumental Alaska lands protection bill passed the House and was sent to President Carter for signature yesterday after environmentalists, gulping hard, bowed to the new Washington political reality and withdrew their opposition.

The measure, which had passed the Senate in August, was approved on a voice vote. Rep. Morris K. Udall (D-Ariz.) called it "one of the most far-reaching conservation decisions in history," but he also said he would be back next year to amend it.

"We are now in a situation where realistically the Senate bill is the only option," he said.

Udall had told a crowded news conference earlier that the Senate-passed package was "a significant step forward" and that he had decided to endorse it despite "deficiencies" he vowed to fight another day.

"I don't like the present version," he said. "I don't claim that this is a great victory . . . but on balance it's the thing to do." It contains 85 to 95 percent of what he wanted and it is just "political reality" to act now, he added.

Shortly after the vote, Carter issued a statement from the White House, saying he was pleased with the approval of the bill and calling it "the greatest land conservation legislation of the century."

The vote ends four years of congressional warfare over the way to balance economic development and environmental protection in more than 100 million acres of virgin Alaska wilderness. As chairman of the House Interior Committee, Udall led the House twice to pass a strongly protectionist measure that the Senate, wanting more leeway for oil and mineral development, was never able to stomach.

This year the Senate wrote its own approach and force-fed it to the House.

The Alaska Coalition of 52 national environmental groups joined Udall in grudging endorsement of the Senate bill, calling it "a major step in the settlement of the Alaska lands issue" despite "major shortcomings."

Sources close to the issue said this outcome was inevitable as soon as the election returns were in. "Nobody needed much convincing" that the Senate bill, already the compromise product of a long struggle on and off the floor, was the best environmentalists were going to get in the near future, said one committee staff member.

All sides emphasized that tinkering with details of the various boundaries and uses outlined for particular Alaska land parcels will continue for some time and may even begin before the lame-duck session ends.

"We're going to try and change 25 percent of it, and they are too," said Sen. Ted Stevens (R-Alaska), who led Senate opposition to Udall's approach. "We weren't overly happy with the bill . . . but it gives us about 80 percent" of what most of Alaska's major politicians had wanted.

The measure deals with more land California and Maine combined, giving Alaska 80 percent of the nation's wildlife refuges and two-thirds of its national parks. It puts 56.4 million acres of untouched mountain range and animal habitat under total wilderness protection that bans forever any kind of mineral or other development.

Another 49 million acres will be given less but still substantial protection in national park or wildlife refuge categories that will allow some mining and timber-cutting activity. It was the detailed breakdown among individual land parcels that made the measure so controversial and tied the Senate in knots last summer.

The architect of the Senate compromise that won final approval yesterday, Sen. Paul Tsongas (D-Mass.), said he had always thought the measure was "realistic about what was possible." s