The incoming Reagan administration -- committed to reducing federal regulations -- will inherit a full plate of pending or just-completed regulatory actions which it can use to demonstrate a new approach to these issues.

The new administration will have a chance through regulartory decisions to influence the evolution of the car and truck industries, the future of economic development in the industrial regions of the East and Midwest, the economic plight of the steel and paper industries and much more in its first months in office.

As these examples indicate, actually cutting out federal regulations will be harder to do by executive fiat than the president-elect might like. At the same time, these current regulatory issues demonstrate the enormous power federal rules-maker can wield under existing legislation.

One new approach to federal regulation proposed by a panel of Reagan advisers -- a one-year moratorium on new regulations -- will prove to be impossible because of outstanding court orders and legislative requirements. Indeed, lawsuits filed to enforce existing legislation are a powerful factor in pushing federal regulators into action, sometimes against their own will.

The most direct way to reduce federal regulation would be to repeal or amend existing laws, but the president-elect has not made any specific proposals to do this.

Here are some of the principal regulatory actions that the Reagan administration will face when it takes office:

A new rule from the National Highway Traffic Safety Administration (NHTSA) establishing fuel efficiency standards for "light trucks" in the 1983-85 model years.

Light trucks, including most vans and pick-ups, consume about 20 percent of the gasoline used in the United States. According to the government, standards requiring better gas mileage for these vehicles would save tens of billions of barrels of oil. New standards would also add to the costs of producing light trucks in the United States.

Joan Claybrook, the current administrator of the NHTSA, said yesterday that her office will be issuing the new fuel efficiency standards for light trucks in the near future. But she acknowledged that her successor in the Reagan administration will have until March of next year -- when this standard must be finally published, according to the statute -- to alter whatever decision is made now.

For American truck-makers, the ultimate decision can mean differences of tens of millions of dollars, perhaps more. The big truck-makers have already indicated that they could accept standards that would rise from about 18 miles per gallon in 1983 to nearly 20 mpg in 1985, but that higher standards would be much harder to meet.

A standard for "heavy-duty diesel particulates" that is required under the Clean Air Act for 1985 models of diesel engines. Particulates are a form of pollutant created in relatively large quantities by diesel engines. The car-makers say that the future exploitation of the diesel engine -- which gets better mileage than standard gasoline-buring engines -- will depend on a "reasonable" government standard on particulates.

A final rule is not supposed to be issued until late next spring, so the new administration will have a clear shot at this one. How it comes out will influence the development of the car and truck industry for the rest of the century.

New standards setting permissible limits for the emission of water pollutants from iron and steel works, pulp and paper plants and steam generated electric power plants.

These are all potentially multibillion-dollar regulations that are scheduled to be issued next spring and summer . The Environmental Protection Agency is under federal court orders to issue all three of these standards, and those orders will apply under the Reagan administration as well.

Officials at EPA say privately that a new administration would have a difficult time satisfying statutes on the books if it sought fundamentally to alter the rule-making procedures already under way in these cases. The agency, they contend, is already following a policy that Reagan has publicly espoused -- measuring the economic impact of new regulations before promulgating them. They describe the rule-making process as "objective" and "fair" and not something that could easily be altered.

However, the Clean Water Act does not specify standards of water purity that must be achieved, leaving some discretion to the EPA in writing regulations that can determine the economic health of some big American industries.

New Federal Trade Commission rules governing the funeral industry, sales of hearing aids and the used car business, among others. All of these are extremely controversial proposals that the industries involved have lobbied heavily against. Michael Pertshuk, current chairman of the FTC, noted in an interview yesterday that all three FTC inquiries were launched more than four years ago, when the commission was under Republican control.

Nevertheless, the new administration and its new FTC chairman may want to alter the approach to all three issues. Since there are no immediate vacancies on the FTC, however, proponents of looser regulation that the commission proposes may wage their battle in Congress instead. Under new legislation, these FTC rulings will be subject to congressional veto.

Later in 1981 the Reagan administration's secretary of the interior will have to satisfy a court order by producing a plan to enforce the Reclamation Act of 1902, the law that was supposed to limit the size of farms benefiting from federal irrigation projects to 160 acres. In fact giant California agribusinesses have managed to put together much bigger farms in irrigated areas.

There are also numerous federal regulations in noneconomic fields that the new administration will be able to modify to suit its policy goals. For example, a Carter administration proposal to require local school districts to provide bilingual educational opportunities, which would have been extremely controversial even if President Carter had won reelection, apparently faces early withdrawal in the Reagan administration.