The Carter administration said yesterday that if Congress doesn't pass the controversial Alaska lands bill this year, it may try to protect the land through administrative action.

Interior Secretary Cecil D. Andrus said that President Carter is "looking into" existing laws that would allow the government to prevent development on roughly 100 million acres of Alaskan wilderness eve if the lands bill is not approved.

The bill has passed the House, but is being held up in the Senate by the Alaska delegation.

On a recent tour in Alaska, Andrus had indicated that the administration might use existing authority to protect the acreage, but yesterday was the first time he had publicly raised the possibility in Washington.

Andrus said the administration was looking into declaring the lands national monuments, under the Antiquities Act, or lands under study by the Bureau of Land Management, under the Federal Land Use Policy and Management Act.

"We're not threatening, but we're looking into" these options, Andrus said.

The bill in congress would double the size of the national park system by setting aside about a third of Alaska for parks, preserves, refuges and wilderness areas.

Alaska's senators and the state's mining, timber and oil interests have fought the 100-million-acre proposal, saying it unfairly limits growth and development. they also say it ties up land that the state could have selected for its own use. Under the 25 years to select 105 million acres for itself - whether for economic development or use as parks. Alaska has selected 30 million acres so far.

Sen. Mike Gravel (D) has threatened to filibuster the bill, Alaska's other senator, Republican Ted Stevens wants to amend the bill in committe. He would protect 804 million acres and opposes designating any as wilderness areas. He prefers setting aside the land as national forests wildlife ranges and "multiple-use parks," where mining, logging and dredging could occur.

Conservationists support the bill. So does the House Interior Committee chairman, Morris K. Udall (D-Ariz.), who says Alaska lands belong to the nation, just as the Gran Canyon does.

The Carter administration also backs the House bill, although its proposal was less ambitious - protecting 92.5 million acres.

The Interior Department could keen Alaska lands as wilderness over the objections of Alaska's sentors by using the 1976 land use act. The act enpowers the Bureau of Land Mancide whether to desingnate the areas as wilderness. 5,000 acres or more before they are classified as wilderness areas. Such a study could take up to 15 years, and then it would be up to Congress to decide whether to designate the areas as wilderness.

In wilderness areas, there are no permanent structures, no roads, and no power boats or automobiles. Hiking and horseback riding are allowed. J. Carnell.

The president could keep federal control over segments of the Alaska wilderness lands by using the 1906 Antiquities Act, which authorizes him to declare up to 5,000 acres as a national monument. Carter could declar several 5,000-acre parcels as national monuments, precluding their development.