Interstate Commerce Commission Chairman Reese H. Taylor Jr., in a letter to President Reagan, yesterday endorsed complete deregulation of the trucking industry--a position the administration had been shying away from for political reasons.

Although Taylor's letter was not made public, an ICC spokesman confirmed the gist of the apparent policy change reported by Rep. Jerry Lewis (R-Calif.) following a meeting between Lewis and Taylor. Lewis is chairman of the House Republican task force on congressional and regulatory reform.

"In Taylor's letter to the president, the chairman states clearly his unqualified support for proposed legislation to eliminate economic regulation of the trucking, freight-forwarder and water-carrier industries," Lewis said. "He thinks the timing is right and he thinks we should move as quickly as possible."

The administration has been going slow on trucking deregulation to avoid angering the Teamsters union, one of President Reagan's strongest supporters in the labor movement. The administration has reportedly already sidetracked a trucking deregulation bill at the urging of the Teamsters, who claim it has cost 300,000 union members their jobs. Teamsters officials could not be reached for comment yesterday on Taylor's apparent shift.

Criticized by some members of Congress for going too slowly on deregulation, Taylor has replied by saying that he wanted to take measured steps toward deregulation to avoid causing disruptions in the trucking industry.

Lewis said Taylor now believes the groundwork is ready. "The commissioner did not seem to be dragging his feet today," Lewis said. An ICC spokesman said the letter to the president did not represent a change in Taylor's position. "It finally will dispel, hopefully, the thought that he has not been pro-deregulation all along," the spokesman said.

Lewis said Taylor indicated in their meeting that he might also support abolition of the ICC, the nation's oldest regulatory agency, although Lewis said he does not believe Taylor suggested that to the president.

Lewis said Taylor has also submitted to the White House a variety of strategies that might be followed to bring trucking deregulation to Congress, ranging from doing nothing to full support of deregulation legislation. "He indicated clearly that he preferred to go all-out," Lewis said.

The deregulation issue has created a split within the administration, with the Department of Transportation backing full deregulation and drawing up legislation, only to have it tabled by the White House.

In the past few years, the ICC has lifted many regulations from the trucking industry, making it easier for new truck lines to enter the market, allowing truckers to change rates without cumbersome ICC proceedings and to contract directly with shippers.

The bill prepared by DOT earlier this year would have totally deregulated the trucking, barge and freight-forwarding industries. Eventually, remaining ICC functions, such as some railroad and interstate bus regulations, safety issues and consumer protection would have been transferred into other agencies and the 96-year-old commission dissolved.