United Airlines, the largest U.S. carrier yesterday asked the Civil Aeronautics Board for permission to raise its fares by a full 9.5 percent on Friday.

United was the first to take advantage of a board decision last week to raise the domestic fare ceiling -- the standard industry fare level -- by that amount.

The 9.5 percent allowable increase is in addition to increases of up to 5 percent airlines have been able to take under a fare flexibility program permitted by the Airline Deregulation Act and by board policy. The program allows carriers to raise fares 5 percent above the domestic fare ceiling. Some airlines have used the 5 percent already while others haven't.

United's request came in a petition to the board asking approval to file its increased fares on "short notice." Normally a fare filing is made at least 30 days in advance of the effective date.

If approved, United said that on Friday, it will begin charging fares that are generally 9.5 percent higher than those currently in effect. Excluded from the increases are fares within the state of California, those between the mainland and Hawaii and those between the United States and Canada.

Passengers already holding tickets for flights on or after Friday won't be required to pay the increased fares, however, United said.

The CAB decision to raise the domestic fare ceiling was based primarily on fuel costs rising more rapidly than earlier anticipated, the board said. It was the third increase in fare levels this year; in May the board permitted a 4 percent increase and allowed a 6.6 percent hike in July.

Although the 9.5 percent boost is only a ceiling and does not mean that fares will automatically rise by that amount and the CAB said it thought competition would determine the fare level on many routes, the big three airlines -- American Airlines and Trans World Airlines in addition to United -- have already said they would utilize the full 9.5 percent.