Because it has less to do as a result of phased-in deregulation of the airline industry, the Civil Aeronautics Board asked to have its funding cut by 7 percent, or $2.66 million, over the next year and a half.

An amendment of fiscal 1979 and 1980 budgets submitted to the Office of Management and Budget also reduces from 819 to 743 the number of staff positions the CAB had origingally requested for the September 1980 ceiling.

At yesterday's White House briefing, administration officials crowed about the reduced fares the airlines are offering the public in an increasingly competitive environment. "Elimination of excessive government regulation is an important and workable part of our attack . . . the structural causes of inflation," press secretary Jody Powell said.

"This demonstrates that it is really possible for the government to get out of a business it is engaged in and serve the public better," added Alfred E. Kahn, the president's chief inflation adviser, who pushed vigorously for airline deregulation as chairman of the CAB.

In other CAB developments yesterday:

A CAB official warned all domestic airlines that they no longer have antitrust immunity to circulate proposed fare changes to other carriers before they are filed with board, "I hope you appreciate the fact that the continued circulation of such information could leave your company and officials open to . . . prosecution," Reuben B. Robertson, director of the CAB's Bureau of Consumer Protection, wrote each airline.

The board this month made final a recission of a long-standing approval of such an information exchange, which had been undertaken by the Airline Tariff Publishing Co.

Robertson pledged "very active" enforcement of prohibitions against price collusion during this early stage of deregulation and said violations could be referred to the Justice Department for prosecution.

A CAB administrative law judge granted new authority to 14 airlines to fly between Chicago's almost unused Midway Airport and 24 cities. Among the carriers that would get new authority are Evergreen International Airlines, Midway Airlines - a corporation now seeking capital and planes, a subsidiary of the Texas-based Southwest Airlines - and Wien Air Alaska.

In his initial decision, which becomes effective in 30 days unless reviewed and modified by the full board, law judge Ronnie A. Yoder found that Federal Express Corp., an all-cargo airline, had not met the board's fitness requirements to become a passenger airline.

A spokesman for Federal Express said the airline would seek full board review.