After dismantling much of the governmental apparatus that for years told the nation's airlines, railroads, trucks and buses where to go, Congress and the Reagan administration are trying to figure out what to do with the transportation regulatory tasks that remain.

Bill writers are considering everything from abolishing what's left of transportation regulation to creating a new regulatory body to handle it all.

They are getting substantial advice from groups such as the conservative Heritage Foundation and the House Republican Research Committee, both of which weighed in yesterday with strong recommendations that deregulation be accelerated.

The central question is how far to go and what to do with what's left. It involves issues such as these:

Who, if anyone, should guarantee that small communities receive essential passenger and freight service?

Who should decide which U.S. airlines get international routes and what fares they (and their foreign competitors) can charge?

Who, if anyone, should decide which railroad mergers are in the public interest?

What can be done to help move cargo that must travel by truck, rail, barge and ship to complete its journey--and make its freight rates more understandable?

The debate comes at a time when the nation's transportation system is being realigned as longtime governmental guarantees for fares, labor practices and routes disappear.

That's fine, both the Heritage Foundation and the House Republicans said, but they expressed concern that the administration seems to have lost some of its ardor for deregulation. Related story, Page C6

"More active leadership is needed if this administration is to complete the job of deregulation by abolishing the Interstate Commerce Commission, the Federal Maritime Commission and the Civil Aeronautics Board," the Heritage Foundation suggested in the transportation chapter of its forthcoming book, Agenda '83.

The House Republican group, headed by Rep. Jerry Lewis (R-Calif.), said in a 42-page report that more needs to be done to allow market forces to reduce prices and improve services.

For example, the report said, "There is little reason for the ICC to continue its existence and a schedule for sunsetting the ICC should be set" before 1987.

The ICC, which regulates railroads, trucks and buses, already has less to do because of three pieces of deregulatory legislation affecting railroads, trucks and buses.

However, the Heritage Foundation said, that trend could change with the membership of the ICC.

"We will only be sure of deregulation if we abolish the agency itself," the foundation said.

The CAB, which once controlled almost everything that the airlines did, is scheduled to go out of business Jan. 1, 1985, and the House Republican group urged that it be eliminated earlier.

The problem is what to do with its remaining functions, including regulation of international air travel.

The foundation said that, because some CAB duties will be transferred to DOT's Federal Aviation Administration, the "airline industry is in danger of being reregulated."

The administration is seeking substantial changes in Federal Maritime Commission regulation of the steamship business and the FMC has already shortened the amount of time it takes to consider industry filings.

It too should be scrapped, the House Republican group said, with essential functions transferred to DOT.

Sen. Bob Packwood (R-Ore.), chairman of the Commerce, Science and Transportation Committee, is planning to introduce legislation that would create a single five-member transportation regulatory commission to absorb the remaining functions of the CAB, the ICC and the FMC.

Packwood, whose committee will hold confirmation hearings for Transportation Secretary-designate Elizabeth Hanford Dole on Jan. 26, mentioned the idea briefly in his first meeting with her since her nomination, and the proposal has been explained to several transportation trade associations in Washington.

Its main advantages, according to advocates on the committee staff, are that a single commission dealing with all transportation issues would be able to attract top-quality people and would ease the regulatory burdens that still hamper shipments that require the use of more than one mode of transportation to get from point A to point B.

Under current regulations, for example, it is impossible for a shipping combine to quote a single rate for moving a container from an inland point in the United States to an inland point in Europe.

A committee staffer said the panel had discovered that one reason for the growth of the so-called piggyback business (truck trailers on rail flatcars) is "because both trucking and railroading were handled by the ICC, and the commissioners could easily see the advantages for both."

The administration would rather place the remaining regulatory functions in DOT, something the House Republican group supported. There is concern on Capitol Hill though that that would violate a principle dating from the creation of the ICC in 1887 that transportation regulation be kept separate from a politicized Cabinet agency.

An example of that concern is the fact that DOT has scheduled a symposium here in March at which aviation industry specialists will discuss ways to insulate international issues from DOT's political atmosphere if the remains of the CAB go to FAA.

Christopher C. DeMuth, OMB's administrator for information and regulatory affairs, said that "in our view, the independent agency concept is out of date; it's largely a relic . . . . " DeMuth said he agrees with one Senate Commerce argument: that a merged agency with more than one industry to regulate is less likely to be preoccupied with just one subject.

"On the other hand," he said, "the idea of creating a new regulatory agency kind of goes against our grain over here." In any case, he said, a detailed administration position will not be developed until Dole is confirmed.