In a rare display of mutual admiration, President Carter and Sen. Edward M. Kennedy (D-Mass.) appeared Rose Garden as Carter signed into law fought for vigorously.

"Well, there's no debate about trucking deregulation," Kennedy joked to the delighted crowd after he was called on by the president to say a few words. Kennedy had spent much of the last eight months trying to get Carter on the same platform to debate him as both sought the Democratic Party's presidential nomination.

Yesterday's signing ceremony was their first public appearance together since last Dec. 9 when both attended a birthday dinner party here in honor of House Speaker Tip O'Neill.

Kennedy, who commended the president for "a very special effort" on behalf of the bill, was a strong supporter of trucking deregulation long before he and Carter teamed up a year ago to support a measure and build a coalition for it -- something Carter acknowledged in his introduction.

"There was one senator who worked on this legislation for at least two years prior to that, sometimes alone, sometimes facing discouragement, but never giving up on the concept," Carter said.

Like the airline and banking deregulation bills already enacted into law during Carter's tenure at the White House and a rail deregulation bill pending in the House, the trucking law is designed to introduce more competition into a heavily regulated sector of the economy.

The new law pares back 45 years of extensive federal regulation of the trucking industry. It will make it easier for new trucking companies to enter the business and for existing firms to expand their services, will give the firms more freedom to raise or lower freight rates without government intervention, gradually will limit the antitrust immunity that now enables competing truckers to agree on prices they will charge, and will pave the way for eliminating many route and commodity restrictions that inhibit fuel-saving and efficient operations.

"This act will bring the trucking industry into the free-market system where it belongs," Carter said yesterday.

"The Motor Carrier Act of 1980 will eliminate the red tape and the senseless overregulation that have hampered the free growth and development of the American trucking industry," he said. By ending wasteful practices and promoting competition, the president said the bill will help in the fight against inflation by reducing costs of products consumers buy, as well as save millions of gallons of gasoline every year.

The ICC has been preparing for the legislation and today is to announce plans for its implementation.

As might be expected, the occasion of the bill-signing was ripe for quips about the rivalry for the Democratic presidential nomination. Before President Carter joined the assemblage of almost 250 in the Rose Garden, the table for the bill-signing had to be raised so that photographers behind the crowd could see it. When it was clear someone needed to sit in the chair to test whether it was high enough, Commerce Committee Chairman Howard W. Cannon (D-Nev.), a chief Senate sponsor of the bill, said to Kennedy, "Ted, why don't you sit down there and see how it fits?"

"I'd be delighted to sit down," Kennedy said, laughing.

Carter's introduction of Kennedy followed words of strong praise for Kennedy's leadership on the trucking issue from Cannon.

"This bill demonstrates how effective the senator can be in developing a controversial issue and working with his colleagues in Congress in implementing comprehensive and effectiver legislation," Cannon said. Cannon, who had teamed with Kennedy on the airline bill, also lauded the president's support and effectiveness on the trucking issue.