Although some communities have experienced a cutback in airline service since the Airline Deregulation Act was passed last year, most communities have gained service, the Civil Aeronautics Board told Congress yesterday.

"The vast majority of passengers and the great majority of cities are receiving the same or more service than they did a year ago," CAB Chairman Marvin S. Cohen said at hearings before the Senate Commerce Committee.

"By almost every aggregate measure, the results of change have been good," he said.

Besides additional service to most airports, Cohen cited increases in the number of certificated airlines, airplanes in service and utilization of planes, more passengers flying more miles than ever before and declining fares for many travelers. In addition, the airlines are making more money than ever and have increased the number of jobs in the industry.

Despite communities' allegations of a decline in services, none of them has lost all service in the last six months since the bill became law, while 129 communities lost all service in the 10 preceding years, Cohen noted. In addition, the provisions of the bill now give the communities notice of an airlines intent to end service, and the CAB has blocked suspensions of service on 25 occasions in the last six months, he noted. The board has the authority to keep a carrier on a route while it seeks a replacement.

Senate Majority Leader Robert C. Byrd (D-W.Va.) opened the hearing with a vigorous denunciation of the effects of airline deregulation, using decreasing service to West Virginia cities as a focal pont.

"Rather than using the loosening of federal regulations to improve services, or to reduce fares through increased competition, it appears that our airlines have in certain instances taken the license now available to them to decrease service and increase fares." Byrd charged. If the legislation were to come up for a vote now, Byrd said he would vote against it.

He also said said he doesn't like using the commuter airlines that in many cases are replacing the larger airlines' service to small communities. "Personally, I've never relished the idea of getting on commuters and I'm not going to fly them any more than I have to," he said. After Senate Commerce Chairman Howard W. Cannon (DNev.) stated that, based on unmber of departures, the safety record of commuters and the trunk airlines are the same, Byrd admitted, "I have not facts on which to justify my fears but I still have them." CAPTION: Picture, ROBERT C. BYRD . . . dislikes commuter airlines