Alfred E. Kahn led a panel of deregulation-minded former regulators yesterday in charging that Interstate Commerce Commission Chairman Reese H. Taylor Jr. has begun to slow the pace of trucking industry reform begun under the Carter administration despite the "proclaimed faith of the Reagan administration in free competitive enterprise."

"I . . . see clear evidences of retreat from free-market principles," said Kahn, the former chairman of the Civil Aeronautics Board. Kahn's remarks were made during an unusual Joint Economic Committee hearing at which the witnesses attacked Taylor's policies, Taylor responded, and the panel of critics returned for a rebuttal period.

Kahn said the ICC under Taylor had begun to interpret its legislative mandate "in a more protectionist, anticompetitive manner" by defining operating authority more closely, requiring "more thorough and precise attestations" from shippers of the need for all of the requested authority, restricting pricing flexibility, and placing increasingly heavy emphasis on the fitness, willingness and ability of an applicant actually to offer on demand all the service described in the authority it seeks.

Kahn, who returned to a Cornell University economics professorship after leaving his post as Carter's anti-inflation czar, laid the blame at the White House. "A president is a president," he said. "And if a president decides sincerely that he believes in free enterprise and believes this industry can be effectively competitive, there's no reason in the world why the ICC cannot be responsive. Ultimately that's where the responsibility lies."

Also testifying were two former ICC members, Thomas A. Trantum and Marcus Alexis. "What we find in Chairman Reese Taylor, who's a very likeable, personable chap, is someone who just is an inveterate regulator," said Alexis, who returned this fall to Northwestern University to resume his job as economics professor.

He was especially critical of Taylor after the Reagan appointee defended his decisions by citing his interpretation of congressional intent and the benefits the trucking reform law already has yielded, and by recounting statistics purporting to show that the ICC has been granting more than 95 percent of the applications filed before it, equalling or bettering the record of the prior commission.

"The chairman has displayed a capacity for taking credit for that which he has not accomplished," Alexis said. He called the statistics on authority grants that Taylor recited "particular misleading."

The applications were often granted "in part," he said, which restricts the operating authority substantially in geography, in commodities that can be carried and in other ways. "There may be a numerical similarity between what went on when I was at the commission and what is going on now, but that similarity is purely superficial; quantities may be similar but the quality of grants has deteriorated," he said.

He also said Taylor's legislative proposals to change the requirements for entry to the trucking industry would be "more restrictive" than the current standard contained in the recently enacted law. "Furthermore, I think it's a cop-out to argue that the commission does not have sufficient jurisdiction . . . to move in the direction of eased entry," he said.

Thomas Gale Moore, senior fellow at the Hoover Institution at Stanford University and an economist with strong Republican connections, also disputed Taylor's contention that the White House was happy with him and that he had sought policy guidance and hadn't been given any. Moore said his contacts with White House personnel had convinced him that "they are in favor of competition and not what he's doing."

Knowledgeable sources have said that Taylor was called over to the White House for a meeting with Presidential Counseller Ed Meese several months ago for the purpose of reminding Taylor that the Reagan administration has a procompetition philosophy.