Some guests walked away from a congressional appreciation dinner given by the American Trucking Associations last year wondering at the significance of an elaborate ice sculpture.

It appeared to show four large trucks backed up against the Capitol -- or was the Capitol actually sitting on the back of four flat-bed trucks, as some thought?

Did the sculpture signify the political clout the trucking industry is thought to have over Congress, hauling it around like that? Or were the trucks, heading in four different directions, about to pull Congress apart?

Whatever the sculpture's deeper meaning, proponents of changing the 45-year-old regulatory mantle governing the trucking industry are hoping the industry's influence, like the ice sculpture, has begun to melt away.

However, the common wisdom is that the trucking industry and its ally in the fight against any deregulation, the Teamsters union, still have enormous influence, especially in the House of Representatives where legislative efforts are considerably less dramatic and substantial than in the Senate. Few congressional districts are untouched by at least one of the 16,000 members of the regulated trucking industry.

Except for the reputed influence of the members of the regulated industry, the congressional debate over trucking deregulation -- or trucking "regulatory reform" as most call it -- has some striking parallels to the debate over airline deregulation, which culminated in the enactment of the Airline Deregulation Act in 1978:

As the Civil Aeronautics Board did then, the Interstate Commerce Commission is moving ahead with deregulatory policies administratively, with strong White House backing both in agency appointments and verbal encouragement.

There is bipartisan support for reform as well as the backing of wildly diverse interest groups, including the National Association of Manufacturers, the American Farm Bureau, Common Cause, American Conservative Union, National Federation of Independent Businesses, the Ralph Nader-associated Congress Watch and Transportation Consumer Action Project.

In general, there is opposition to deregulation from the industry and its unions but there are some significant exceptions; some segments of the trucking industry -- just as did some segments of the formerly compartmentalized airline industry -- want looser government controls in order to expand their operations and take advantage of new opportunities.

In trucking, the "unregulated" independents would like a legal crack at business now out of reach because it can be carried only by the regulated companies; regulated trucking companies operating only under "contract" also want an end to limitations on their options; minority truckers want easier excesss into the industry; private carriers like Sears, Roebuck & Co. and other corporations want some restrictions on their activities lifted.

There also are uncanny parallels in the way the trucking measure is working its ways through Congress: In both airline and trucking, there were early pushes by Sen. Edward M. Kennedy (D-Mass.) for reform. In the airline area, Kennedy held hearings on the CAP as chairman of the subcommittee on administrative practice and procedure, and he became a believer in deregulation. As chairman of the anti-trust and monopoly subcommittee, he held hearings on competition in the trucking industry in 1977 and 1978 and became a believer.

As in the airline debate, so in trucking Kennedy and Sen. Howard W. Cannon (D-Nev.) have had their disputes. In aviation, Kennedy was pushing the measure before Cannon -- then chairman of the aviation subcommittee -- was ready; they would not co-sponsor the measure that was passed. On trucking, Kennedy was pushing forward while the Senate Commerce chairman was still in his "open mind" period, promising all sides a "fair hearing" on the issue. After extensive hearings, Cannon decided he was for reducing regulation, and has begun to move forward under his sponsorship a measure that deregulators are cheered about.

Although similarities abound, whether the outcome is the same is still to be determined.

Proponents, however, are optimistic. Cannon has pledged to the White House that he will try to get a trucking reform bill on the president's desk by June 1. With Sen. Bob Packwood (R-ore.), ranking minority member of the committee, Cannon has introduced a bill he hopes to begin marking up Thursday.

The bill would do all the things the regulated industry and the Teamsters don't want done, and it stops short of the measure jointly sponsored by Kennedy and the Carter administration, although sources for both say the Cannon-Packwood measure would be signed into law if it came to the White House intact.

The measure would make substantial changes in the way the Interstate Commerce Commission regulates trucking in an effort to make industry members increasingly more reliant on the marketplace and less on government regulation in its decision making.

Responding to shipper's pent-up demand for new services, the ICC already has begun loosening some restrictions. The commission recently has begun making it easier for new companies to start and for existing companies to expand.

Specifically the commission is giving greater weight to competition, has allowed companies shipping goods on their own trucks to carry goods in any direction, has eased requirements for truckers who want to provide services to the federal government and has ended the limits on the number of shippers with whom a trucking company can sign contracts.

There are also numerous proposals pending that similarly would alter the way trucking companies have done business over the years. In an attempt to reduce energy consumption, for instance, the ICC proposed allowing trucking firms to serve temporarily any intermediate points on their authorized routes. Certificates now often prohibit companies from picking up freight at stops, however small, along the way that aren't specifically authorized.

The agency also proposed to relax its prohibition on an affiliate of a company carrying freight for another affiliate, even for compensation. Under the proposal, "intercorporate hauling" would be permitted when transportation would be provided by the parent company or a related company owned at least 80 percent by the parent.

The agency also has begun to consider ways to encourage the industry to come up with more variety in pricing and services. Last month it unveiled a proposal designed to increase rate competition among regulated trucking companies by establishing a zone within which carriers could raise or lower rates without ICC interference, But the rates in the zone would have to be independently and not in the rate bureaus that now have the legal right to price-fix, and use it.

The Cannon-Packwood bill also would make it much easier for companies to enter the trucking business and for existing trucking companies to expand their services. It would give trucking companies some pricing freedom: they could raise and lower rates within a certain range without ICC intervention. The bill also would open to public scrutiny the rate bureaus used by the trucking industry to jointly set the fees they all will charge. The measure in fact would eliminate next year the antitrust exemption that allows trucking firms to jointly set rates for single-line shipments -- those in which a company picks up and delivers the goods on its own authority without transferring the shipment to another company.

The measure also sets up a schedule for eliminating restrictions that are though to inhibit efficient and fuel-conserving operations of companies, such as requiring a truck driver to follow a specific route instead of the most direct and fastest.

Expedited ICC procedures for eliminating other restrictions also are mandated, as are streamlined agency procedures and deadlines for actions.

The ATA and the Teamsters, to say the least, aren't happy about the bill Cannon came up with. For instance, Teamsters Union President Frank E. Fitzsimmons told Cannon in a telegram that the bill is "completely unacceptable, and we will expend all our effort to have this measure changed."

"If enacted into law, the proposal will result in complete destruction of qualified motor carriers who now employ over 50,000 of our members," he wrote. The Teamsters have been threatening to defeat at the polls anyone in favor of the measure.

On the house side, Rep. Harold T. (Bizz) Johnson (D-Calif.), chairman of the Public Works and Transportation Committee, and Rep. James Howard (D-(N.J.), chairman of the surface transportation subcommittee, also promised the White House to have the legislation ready June 1. Working with the Senate side, they have introduced a measure described by a Senate source as "90 percent similar" to the Cannon-Packwood measure.

But the 10 percent difference is significant: there would be more restrictive entry policies and no lifting of any antitrust immunity for price-fixing, for instance. Although the ATA said it doesn't like the House measure, it is expected that they could "live with it," according to a transportation source.

The White House and the ICC couldn't live with the House measure, however. Recently, White House officials met with ATA officials -- for the second time in severa weeks -- and suggested the president definitely would veto the House measure should it come to his desk. Although he prefers the Carter-Kennedy bill, he would be satisfied with the Cannon-Packwood measure, the trucking industry and Commerce Committee were told.

President Carter and his aides have made it clear numerous times that he wouldn't sign a bill that freezes the system as is or decreases the amount of discretion the ICC has to make changes on its own.