"Is a puzzlement," the king said in "The King and I."

That assessment, repeated by a railroad expert about the outlook of the rail industry in 1980, applies equally to other major components of the transportation services sector -- airlines and trucking companies.

The unknowns of the economy, fuel prices and supplies, and a changing regulatory and legislative picture make uncertainty the watchword in transportation as the decade begins.

As the airline industry proceeds along the deregulatory path laid out for it by Congress in late 1978, it is believed likely that regulatory restraints also will be loosened for railroads and trucking companies.

The best guess is that the railroad industry, which supports deregulation, will get less than it wants in the way of reform and that the trucking industry, which opposes deregulation, will get more than it wants.

But the degree of change and congressional involvement remain unclear.

Congressional intentions are clear; key leaders in both the House and Senate, with the administration's support and urging, have made pronouncements about enacting separate rail and trucking measures that would update the decades-old statutes that govern federal regulation in both industries. But agendas and deadlines often fall by the wayside, especially in an election year, not to mention one that is starting off with foreign affairs preoccupations.

With a new session about to start later this month, the Senate appears to be farther along with transportation legislation. Last year, the Senate Commerce Committee reported out a rail bill, though it is far less radical a deregulation measure than the administration and the railroad industry had hoped for.

The bill would give railroads limited flexibility to raise some rates without interference from the Interstate Commerce Commission but it does not go as far as the administration would go in giving the rails freedom from overall regulation. Still the industry supports the measure as a step in the right direction, and the measure undoubtedly would get the president's signature if it could not be improved on the floor, in the House, or in conference.

Complicating the picture, however, is an amendment now proposed by Sen. Russell Long (D-La.) that would put a cap on rates the rails could charge for moving coal. Although ostensibly designed to help consumers of utilities, opponents of the amendment argue that singling out a commodity for special treatment defeats the purpose of the measure and also probably would be counterproductive to Long's goals. The administration, the industry and Commerce Committee Chairman Howard W. Cannon (D-Nev.) oppose Long's proposal.

In the House side, there is some talk of combining the several rail measures that may get attention this year -- deregulation, Conrail funding, Northeast Corridor and rail retirement provisions -- a move that would complicate and might doom prospects for any significant action.

On trucking, Sen. Cannon set June 1 as the target date for placement of a trucking measure on President Carter's desk for signature and several months ago told the ICC not to make any permanent changes in trucking legislation until after that. Cannon is expected to introduce, perhaps with others, a bill soon after the Congress returns that would reduce regulation of the industry. But again, the bill is not expected to go as far as the measure promoted last year jointly by President Carter and Sen. Edward M. Kennedy (D-Mass.).

The Cannon measure is likely to put into law the initiatives undertaken by the ICC over the last two years and make it easier for new trucking companies to enter the business. But it's unlikely that the measure will remove the antitrust immunity the trucking companies enjoy to sit down and jointly set rates they all will charge.