Interior Department officials are preparing to eliminate wilderness protections from about 800,000 acres of wild lands in the West, contending that the areas do not qualify for the stringent restrictions prohibiting development on them.

In a set of directives to western field offices, Interior also instructed its staff to consider dropping wilderness protections from about 70 other areas, estimated to cover between 1 million and 1.5 million acres in nine western states.

Interior officials said the changes are closely tailored to recent legal rulings by the agency's Board of Land Appeals and will not automatically open the areas to development.

But environmentalists and congressional wilderness advocates denounced the moves as a "midnight attack" on the agency's wilderness study program, under which Interior was directed to review 24 million acres of roadless lands for possible inclusion in the federal wilderness system.

The directives will remove from the study program several famous scenic and recreational areas, including Wyoming's Encampment River Canyon and New Mexico's Bisti Badlands, an expanse of toadstool-shaped rock formations that resemble a moonscape.

"This shows clear contempt of Congress," said Terry Sopher, a former official of Interior's wilderness program who works for the Wilderness Society. "Congress sent a clear message to Secretary James G. Watt in this session to leave our wild areas alone, and right after they go home, he puts a large amount of the wilderness study program in jeopardy."

Interior officials said, however, that the changes are based on an opinion by the agency's solicitor, William H. Coldiron, who said several categories of wild land under study do not meet technical and legal criteria of the study program.

Under that program, Interior was to study 24 million acres of roadless lands designated by the Carter administration as having "outstanding" potential for solitude and recreation, and to recommend to Congress whether to protect them permanently as federal wilderness areas or open them to other uses.

During the study phase, federal law requires Interior to manage the areas as wilderness areas, banning development and motorized traffic, and to submit final decisions on the status of the areas to Congress for approval.

However, Coldiron's opinion cited three recent rulings by Interior's Board of Land Appeals indicating that certain wild lands do not belong in the program.

According to the opinion, federal law does not cover areas of fewer than 5,000 acres, areas where the federal government owns the land surface but not the minerals beneath it and areas singled out for study because of their proximity to other wilderness areas rather than on their own merit.

Interior will drop these areas from the program through regulatory changes exempt from congressional review, officials said.

The first change, dropping the areas under 5,000 acres, is to be published in the Federal Register later this week and take effect immediately, they said.

It will delete 667,587 acres from the study program, including 123,000 acres in California and smaller areas in Arizona, Colorado, Idaho, Montana, Oregon, Nevada, New Mexico, Utah and Wyoming, according to the announcement prepared for the Register.

This change will eliminate the 3,520-acre Bisti Badlands, recently recommended for wilderness protection by an Interior field office in New Mexico.

Other changes are to be published after further study by Interior's field offices, officials said.

They estimated that the areas with split ownership could cover as many as 464,975 acres and that about 1 million to 1.5 million acres would not meet wilderness criteria on their own.

Altogether, they said, the changes could remove more than 2 million of the 24 million acres from the study program.

Interior officials stressed in their directive that areas being deleted from the wilderness study program could be protected under other programs as recreation areas, areas of "critical environmental concern," national register sites, national scenic areas and others.