General Motors Corp. is proposing a very different kind of "rebate" -- one it claims will be worth as much as $350 on future year cars if Congress rolls back controls on two major kinds of auto pollution.

Relaxing the auto emission standards for carbon monoxide and nitrogen oxides (NOx) would permit GM to remove several key pieces of pollution-control equipment installed on most 1981 and new, 1982 model-year cars, producing savings between $165 and $350 per car, GM said, promising to pass these to consumers.

GM is supported by the rest of the domestic auto industry and by President Reagan's new leaders at the Environmental Protection Agency, with both groups saying the changes would cause "relatively small" air-quality problems, if any.

But that claim was challenged at House hearings this week by an internal EPA staff report obtained by Rep. Henry Waxman, (D-Calif.), chairman of the health and environment subcommittee of the Energy and Commerce Committee.

Speaking for the administration, Kathleen M. Bennett, an EPA assistant administrator, told the subcommittee Wednesday that most areas of the country comply with the health-based air quality standard for NOx, and "the remaining problems are limited in number and relatively small."

The "draft" EPA staff analysis, which Bennett said she had not seen, warned that although assessments of the future NOx problem are very uncertain, the "best single" forecast indicates widespread violation of the health-based NOx limits in more than a dozen of the largest cities by the end of this century, with the problem worsening with each year.

"In other words, not only must the auto standard not be relaxed, but the other NOx standards for light and heavy trucks must be made more stringent," concluded the study, prepared by EPA's senior technical experts.

The auto industry's campaign for lighter pollution standards also is opposed by a group of companies that manufacture the sophisticated catalytic converters now used to break up carbon monoxide and nitrogen oxides into harmless exhaust gasses.

The Manufacturers of Emission Controls Association, having hired several top EPA experts who left the agency after the Reagan administration took over, argue that rolling back existing standards would sacrifice needlessly the vital technological breakthroughs in pollution control and increase the risk of serious air pollution hazards in some of the nation's largest cities (while also doing these companies out of millions of dollars in equipment sales).

And so the stage is set for one of the most important regulatory battles of the year, with the auto industry and its allies pushing for immediate action, their opponents pushing back, and the congressional Democratic leadership eyeing the fight as a potent issue to use against President Reagan in the 1982 congressional elections.

The debate is sharpest over the control of nitrogen oxides, a byproduct of gasoline combustion that can injure the lungs and causes acid rain and smog.

The emission limits for NOx were tightened on the 1981 model year cars, requiring cars to discharge no more than one gram of NOx per mile instead of the 2-gram standard that applied to 1980 models.

This compelled several changes in control systems, particularly on larger cars, which increased vehicle costs by an average of $440, GM says.

If the NOx standard were rolled back, beginning with the 1983 models a year from now, auto manufacturers could remove an oxygen sensor, install a simpler carburetor than the current version that is run by a microcomputer, and return to a simpler, less expensive catalyst. On small cars the microcomputer might be removed.

These steps would save money, says John P. DeKany, a former top EPA official, now a consultant for the emissions controls manufacturers. But those systems are the key to future improvements in pollution control, performance and better gasoline mileage, he said.