The Federal Communications Commission is facing tough decisions later this month on who should get the rest of a dwindling supply of radio frequencies allocated for mobile communications for television stations, cellular mobile telephones and two-way mobile radio systems.

Two-way mobile radio systems are used by government agencies, television stations, industries, utilities and public safety agencies such as police and fire departments for private communications. Cellular mobile telephones are used primarily by businesses and operate over radio signals switched between transmitters as cars or people travel.

Nine groups representing business, government and consumer interests have applied for the remaining frequencies, said Robert Foosaner, chief of the FCC private radio bureau. Satisfying their demands would require more than twice as much capacity as is available, he said.

"It's a very difficult decision," Foosaner said. "Each one of the nine petitioners has some valid need for the frequencies, and there are difficult competing interests."

He said the problem is that there simply aren't enough radio frequencies to accommodate expanding services. Consumer and business demand for new radio frequencies no longer will be met by the early 1990s in such cities as Washington, Philadelphia, Houston and San Francisco, Foosaner said. Additional frequencies for two-way radio communications already are needed by the New York City, Los Angeles and Chicago fire and police departments, he said.

Some of the factions warring over remaining radio frequencies are the Land Mobile Communications Council, which represents a variety of land mobile service users; React International Inc., a public service organization providing emergency communications services; and the National Aeronautics and Space Administration, which, together with private companies, wants to launch a satellite-operated mobile telephone service for rural areas, Foosaner said.

The issue is boiling down to a tug of war between the Land Mobile Communications Council and React International over who should benefit from the allocation. "Once again, personal radio users are being outshouted by the commercial interests whose products and services cost more and are less available to the majority of the American people," said Gerald H. Reese, executive director of React International.

Reese said a two-way radio system that, unlike citizens band radios, can connect into the local telephone network could cost about $500, as opposed to about $2,000 for a cellular mobile telephone and about $1,000 for a two-way mobile radio now in use at fire and police departments. The radio would be used by school buses, the elderly or the handicapped for personal communications.

The Land Mobile Communications Council argues that industrial and public safety requirements are more important than the creation of a new radio frequency for consumer use with an untested demand.

"These are not clear-cut, easy decisions, but the commission is going to have to put priorities on which are necessary and less necessary services," said the FCC's Foosaner.