Most federally funded construction of highways and sewage treatment plants has been halted in the Los Angeles and San Francisco areas because the California legislature adamantly refuses to require automobile owners to have their cars inspected and fix those that pollute too much.

Kentucky is barred for the same reasons from spending federal money on highway projects in two suburban Cincinnati counties.

And in Pennsylvania, the legislature punctuated its opposition to an auto inspection program by overriding Gov. Richard L. Thornburgh's veto. Citizens sued, pointing to a 1978 consent decree in which the state agreed to an exhaust inspection program, and the issue is in the federal courts.

The Clean Air Act is responsible for all of this because it says states that have metropolitan areas with fouled air must require inspections of their residents' automobiles. If the car emits more pollutants than regulations specify, it must be repaired.

If the states don't put inspection programs in place, EPA can impose sanctions such as withholding funds for highways and sewage treatment plants, as the Carter administration did in California and Kentucky.

Just last week the Reagan EPA threatened metropolitan areas in 11 states with yet another of the penalties available, a ban on construction of any new facility that would produce hydrocarbon pollution--even those built without federal funds.

So complicated have our politics become that the latest threat, which one might expect environmentalists to applaud, is viewed instead as a political ploy by the administration to pressure Congress to water down the Clean Air Act, now the subject of a major congressional fight.

EPA spokesman Byron Nelson denied that implication. The suspicion arises, however, because the administration has been unable to shake the perception it is soft on the environment. Yesterday, for example, health groups and members of Congress said EPA documents show the agency intends to weaken clean air rules by increasing from one to five the number of times a year a city will be permitted to violate the carbon monoxide standard.

EPA's Nelson said a change is under consideration, but no decision has been reached. Story, Page A18

While the wars continue in Washington, the effects are felt in the land. The California case is among the most interesting because California has the nation's most publicized air pollution problem and a devotion to automobiles and freeways.

California has developed standards that require new automobiles sold in the state to meet tougher emissions rules than the federal government's. "What we have in California," said an EPA official who asked not to be identified, "is a state legislature that is perfectly willing to place stringent requirements on automobile manufacturers but unwilling to inconvenience its voters."

The legislature is scheduled to vote again in June on a proposal to set up inspection and maintenance stations, but in the meantime more than $800 million in highway and sewage treatment projects have been deferred, with the state's two largest cities taking the brunt of the cuts. The California arm of the American Automobile Association is leading the charge against the program.

The importance of exhaust inspections to clean air programs is demonstrated in EPA data. Federal standards require 1981 models to emit no more than 3.4 grams per mile (gpm) of carbon monoxide. (Proposed Clean Air Act amendments that the administration supports would relax that standard to 7 gpm.)

What is important to air quality, EPA argues, is not the new car standard, but what the car does after it has been on the road for a while, after the spark plugs have collected a little gunk and carburetor adjustments have slipped. The average for all cars on the road, EPA estimates, would be 26 gpm without an inspection and maintenance program.

"Unfortunately," the EPA source said, "this has turned into a people's rights vs. states' rights issue, instead of a helpful discussion on whether the standard is good for clean air."

In Kentucky, the state highway department has spent $3 million of its own to keep a road-building program going in Kenton and Campbell counties after federal funds were withdrawn. A big $100 million project is planned for next year with no federal aid.

Pennsylvania has multimillion-dollar road programs scheduled for both of its big cities, where bridges are falling down and long-promised freeways are ready to be built. This year's federally aided contracts were awarded, with the permission of a federal appellate court that still has to consider the merits of a lower-court ruling blocking the projects.

Virginia already has an inspection program in place; a mandatory program will begin Jan. 1 in the District, and Maryland delayed a program for six months that was to begin in July. In other words, elections will be over before the issue has to be tackled again.