The Interior Department has acknowledged that several of its proposals to relax federal strip-mining regulations could pose serious environmental threats to coal-field communities, national forests and wildlife populations.

The threats are detailed in a study prepared by Interior under a settlement with environmentalists who challenged the rule changes in court. The agreement required Interior to catalog all possible environmental impacts of its proposals, including "worst case" scenarios.

While it termed most of the changes harmless, Interior's study said some of its proposals could have extensive repercussions. The "worst case" scenarios include:

* More than 1 million acres of national forests and wildlife refuges where strip mining is now banned could be opened to mining. "There is a considerable potential for either a large amount of land to be mined or an area of national significance to be mined," the study concludes.

* Mining companies could set off explosives at night, a practice prohibited under current regulations. "People living close to mines might experience discomfort or irritation," the study says.

* It would be more difficult for coal-field residents to block mining projects considered threatening to "recreational, scenic, wildlife and cultural resources," the study says. "As a result, there would be an increased risk that mining on state and private lands would irreparably damage those resources."

* Power poles on mine sites would no longer have to be designed to prevent the electrocution of birds that use them as perches. "An increased number of hawks, eagles and falcons would probably die at or near mine sites," according to the study.

Interior officials stressed that the rules are still in preliminary form, and several versions are being considered for each. The "worst cases" apply only to the most extreme options, these officials said.

"None of these are necessarily going to happen. They're just proposed options," said Frank Anderson, an official in Interior's Office of Surface Mining who helped prepare the study. But Interior is not required to drop any option on the grounds that it could cause disruptions, he added.

Despite the catalog of possible threats, the study was branded a "whitewash" by the environmental group whose lawsuit led to it.

"This is not an environmental impact statement, it's a cut-and-paste version of old documents that we felt were inadequate to begin with," said National Wildlife Federation attorney Norman Dean. "They've slanted it to say their regs are harmless and yet they've ended up saying the impacts will be significant. What they really have in these rules is a proposal to gut the federal strip-mining act."

Interior officials say the opposite. "The ultimate purpose in proposing these revisions is to make the process of regulation work more effectively," the study says, "notably, to revise regulations that impose undue burden on industry and the states with no corresponding benefit to the environment."

Interior Secretary James G. Watt has championed the rule changes as a key front in the Reagan administration's "regulatory reform" campaign. He described dozens of the original rules, adopted by the Carter administration, as "excessive, burdensome or counterproductive."

The surface-mining staff has spent the last 18 months rewriting regulations governing everything from the hours when mining companies can set off dynamite blasts to the species of grass to be planted on reclaimed hills.

The original rules were adopted soon after passage of the 1977 Strip Mining Control and Reclamation Act, a landmark measure forcing mining companies to restore hills and mountainsides to their natural state after stripping them of coal. The rule changes are intended to increase "flexibility" for companies and state regulators to meet the goals of the act, Interior officials say.

The proposed changes have been published a few at a time over the last several months, with the last ones scheduled to appear later this week. Many would delete or relax strict design criteria for strip-mine operations, substituting what is known in regulatory jargon as "performance standards."

For example, the new proposals would require mining companies to "minimize disturbances and adverse impacts" on fish and wildlife, deleting sections of the original rules telling companies how to do it. This was the change cited by the study as posing the danger of electrocution to birds flying over mine sites, since it would do away with a requirement for how power poles must be designed.

Rules aimed at controlling erosion, siltation of streams, flooding and other disruptions to land and communities near strip mines are being similarly revised.

Other major proposals would narrow the definition of "citizens' rights," a key battleground between the mining industry and conservationists during the bitter struggle for the strip-mining law. That law essentially deputized coal-field residents as a grass-roots enforcement squad, empowering them to monitor mine sites and petition to have certain lands declared off-limits to mining "where other values are found to be more important."

One proposed rule change would prevent citizens from petitioning to stop mining on federal land. Interior's study notes that a citizens' petition protected federal land within view of Utah's prized Bryce Canyon National Park from being strip mined in 1980.

Another, citizens' groups say, would prevent many coal-field residents from petitioning to prevent mining on state or private property near their homes as well, if they rent rather than own.

Other proposals would give mining companies broader rights to develop national forests and wildlife refuges. The old rules banned mining on such lands unless a company had already bought rights to the coal beneath them on the day the surface-mining act was passed (Aug. 3, 1977), and had obtained permits to develop them or adjacent tracts by that date.

Under a proposed rule change, companies would be required only to have purchased the coal by that date, not to have obtained permits--a change the study estimated could open more than 1 million acres of protected forest and wildlife refuge to mining.

Under the court settlement, Interior is required to accept public comments on the new rules for 60 days and then prepare a final environmental impact statement and the final rules. The new rules could take effect by November, barring further court challenges. But officials at both Interior and the Wildlife Federation say they do not believe the legal battle is over.