The national agonizing over energy needs versus environment protection reaches a sort of turning point this week as the Senate takes up the Alaska lands bill, deciding the fate of more territory than the states of California and Maine combined.

President Carter has called the measure the environmental vote of the century, involving a chance for once to save the breathtaking scenery and numberless wild creatures of a virgin land before the rapine begins. He has promised conservationists he will veto any measure that is not protective enough.

But a small Kuwait of oil is also at stake, along with glittering mineral wealth and timber for millions of homes. More than any measure since the Homestead Act or the opening of the West, the Alaska lands bill is a test of how much environmental protection Americans think is enough.

Acreage is really not the issue, according to all sides, although the area involved is monumental. The Senate Energy and Natural Resources committee package assigns varying degrees of protection to 102 million acres, while the opposition version, backed by the Carter administration, generally is more restrictive for 125 million acres. The acreage difference is about the size of the state of Indiana, but that is less important than the labels to be slapped on each acre.

The land parcels, many the size of smaller states in the "lower 48," are scattered across Alaska's five time zones and include virtually none of its 460,000 people, most of whom live in Anchorage and Fairbanks.

The parcels do include what more than one awestruck observer has called the crown jewels of the entire American continent: soaring Mt. McKinley locally known as Denali; the glacier-studded Brooks Range of mountains north of the Arctic Circle, home of grizzlies and polar bears, caribou and wolves; and the Wrangell-St. Elias park of crevasse and crag and curled-horn Dall sheep on the Southeast coast.

To the William O. Douglas Arctic National Wildlife Range in the northeast the world's largest caribou herd returns each year to bear its young. The Yukon Flats are nesting ground for two million ducks and 16,000 geese. The mighty Yukon River rolls 1,265 navigable miles from one side of the state to the other.

Chunks of these national wonders and much more will be gerrymandered this week into and out of a spectrum of protective categories whose detailed distinctions would rival those of an arms treaty. In every case, the debate will turn on the relative vlaue of resources waiting in the earth.

"We want a bill," Interior Secretary Cecil D. Andrus told reporters last week. "There will be movement among the major amendments."

The committee measure, to be defended by its chairman, Sen. Henry M. Jackson (D-Wash.), is a 125-page rewrite of the environmentalists' delight that passed the House last summer. Most Alaska politicians condemned the House package as a lockup of 40 percent of the state, and the legislature appropriated $3.4 million to fight it. The Jackson bill retains many more options than the House did for future oil and minerals exploration and possible development, but remains a strong environmental protection measure, according to its backers.

We should have the right to continue our lifestyle and traditional means of access," argued Sen. Ted Stevens (R-Alaska). "This measure doesn't go as far as extremists want but it will double the area of the national parks and do the same with the wildlife refuges, triple the existing wilderness . . . eight of the 10 largest parks in the country will be in Alaska."

Environmentalists have mounted their heaviest lobbying effort in memory to restore the House provisions. "This is our last chance to do it right the first time for once," said Charles Clusen, head of the Alaska Coalition. This ad hoc alliance of 52 national groups and scores of local organizations argues that Jackson's package opens too many doors too widely to too much development.

"It leaves things half-protected," said the coalition's Betsy Johnson, "and that's like leaving half the ingredients out of a cake: you just get nothing." The coalition backs five complex amendments from Sen. Paul Tsongas (D-Mass.) that would restore the restrictive "wilderness" and "wildlife refuge" designations to areas the committee measure leaves more open. "

Failing those, a package substitute bill sponsored by Tsongas and Sen. William V. Roth (R-Del.) that would do much the same thing will go to the floor for an up-or-down vote at the end of the proceedings. Then, of course, there is the House-Senate conference, and finally the possibility of a presidential veto, which all combine to make the coalition optimistic.

Stevens, who will be influential in the debate as Senate minority whip as well as an Alaskan voice, said last week he will oppose the entire bill if any Tsongas amendments pass. And that, he added, will be the fault of Alaska's other senator, Democrat Mike Gravel, who doesn't like the idea of any bill at all.

"He won't say what he does want so he leaves [other senators] with no alternative but to go with Tsongas," Stevens said. "If we don't have the votes it'll be because he didn't get them from his side of the aisle."