The Federal Communications Commission ignored its chairman, its staff recommendation and the Justice Department yesterday, and voted a major victory for the Bell System and the rest of the nation's telephone industry by upholding an earlier decision to grant them half the available radio space for revolutionary mobile phone systems.

By a 5-2 vote, the FCC endorsed a position advanced primarily by FCC member Joseph Fogarty, who argued that further revisions in the cellular radio plan would delay a new and very lucrative technology that had been awaiting commission approval for more than a decade. FCC Chairman Mark Fowler and member Anne P. Jones opposed the action.

The vote also ignored an aggressive lobbying campaign by representatives of a variety of radio carriers and other communications concerns, who argued that the system approved by the FCC was a giveaway primarily to American Telephone & Telegraph Co. The Bell System stands to capture a significant slice of the emerging mobile telephone business as a result of the decision.

However, Rep. Timothy Wirth (D-Colo.), chairman of the House telecommunications subcommittee, already has introduced legislation to reverse the decision. The decision also is certain to face a court challenge.

At issue are charges concerning the fairness of the FCC's order in April that split between local telephone companies and radio common carriers--the existing mobile radio firms--the operations of two of the new cellular systems in each city.

When these systems are widely operational, they will expand sharply the extremely tight mobile telephone market. In cellular technology, relatively small areas, or cells, in a city are served by individual radio frequencies, and as a vehicle moves through a community the call can be switched from cell to cell. Thousands of calls can be handled simultaneously in a metropolitan area, while at present mobile systems are extremely limited.

The FCC's Common Carrier Bureau concluded that the split system would grant "significant new monopoly power to AT&T in the top markets," the primary reason Fowler and the Justice Department vehemently opposed the plan. Instead, the bureau proposed that all interested firms seek licenses for the systems on equal footing and that those applications be evaluated on an expedited basis.

But Fogarty said in an interview that under the bureau's plan "this wonderful technology would be delayed for another decade" and said the charge concerning AT&T's significant expansion of power was "facetious and fallacious."

"Our job is to regulate so the American people can get this service fast," Fogarty said. His view was echoed by AT&T.