The Environmental Protection Agency is considering a major relaxation of its auto-emission standards in an attempt to settle eight lawsuits filed by the auto industry.

Government and industry sources said yesterday that current negotiations to end the suits challenging antipollution standards issued during the Carter administration could ultimately change a variety of rules, ranging from mileage testing procedures and warranty requirements for antipollution parts to emission standards for light and heavy-duty trucks.

The settlement agreements, all of which would be contingent on EPA's relaxing the rules, would make it less onerous for the automobile industry to comply with federal environmental standards. If EPA failed to change the rules through subsequent rule-making procedures, the agreements would be voided and the lawsuits would continue, attorneys said.

Negotiations, which are near completion in some of the cases, began at the request of the auto manufacturers last April, about the time President Reagan announced a major relief package for the ailing auto industry, a package that among other things promised to relax dozens of federal rules affecting the industry.

The settlement discussions didn't come to light, however, until earlier this month when General Motors Corp. and Ford Motor Co. filed a motion to defer oral arguments in one of the lawsuits on grounds the suit was "presently the subject of negotiations . . . . The possibility of resolution by agreement will be enhanced if oral argument herein is deferred indefinitely."

The motion was denied by the 6th U.S. Circuit Court of Appeals in Michigan, so oral arguments will go forward this Monday. However, EPA and auto company lawyers say that will not preclude a settlement.

"I perceive that the negotiations are an effort by manufacturers to relax requirements that they felt probably wouldn't get relaxed in the courts," said a former EPA lawyer who was familiar with the settlement talks.

In the past, the lawyer said, the manufacturers were unsuccessful in getting EPA to make the changes they wanted. But with the new administration, "the manufacturers accurately sensed that the agency was in a mode to provide regulatory relief"--so much so that their initial negotiation stance was to ask for a reduction in the current auto pollution standards.

An EPA official who declined to be named said, "There was really nothing sinister or mysterious about the talks; they are all part of the normal procedure around here. Anything that comes out will have to go through public comment."

Nonetheless, Clarence M. Ditlow, director of the Center for Auto Safety, an activist "public interest" group, charged: "EPA is using the settlement process to sell out sound environmental requirements . . . .It's a very clear and sticky way to wipe out the rules."

Among the rules at issue are:

EPA's fuel-economy tests. EPA had tightened its testing procedures to make mileage-per-gallon results a more realistic reflection of what drivers actually experience on the road. However, GM and Ford have complained that the changes are not only illegal but also unfairly and adversely affect their cars' fuel-economy ratings.

Certification regulations for replacement parts to make sure they won't adversely affect auto-emission standards. The Specialty Equipment Manufacturers Association charges these rules are too onerous.

Warranty rules for faulty auto-emission equipment. The Motor Vehicle Manufacturers Association has charged that not only are too many parts covered by these rules but also that manufacturers are being held liable for failures that aren't their fault.

Emission standards for 1984 light and heavy-duty trucks. The lawsuit involving this standard has been put in abeyance since EPA's announcement that it is considering a 60 percent reduction in the standard to save manufacturers from having to install on these vehicles the catalytic converters now used on automobiles. A Senate Environment Committee vote this week, however, would bar the EPA from making such a change, probably leading to a renewal of the suit.

High-altitude rules that make manufacturers liable for any cars sold in cities such as Denver that don't meet the stricter high-altitude rules. Under a settlement that is "99 percent complete," according to one of the lawyers involved, the manufacturers no longer would be liable for the failure of their dealers to adjust cars to meet the special standards.