Telephone bills in Salt Lake County likely will rise by 12 cents per month soon - an increase officials say is needed to keep the 911 emergency system solvent.

State law allows county governments to tack up to 50 cents onto each phone bill for 911 costs. So far, Salt Lake County residents have been paying only 38 cents. Weber, Davis and Utah counties already charge 50 cents, said Salt Lake County Fire Chief Larry Hinman.Without the increase, Salt Lake County's system will run out of money by the end of this year. The increase will keep it going at least until the end of 1995, Hinman said.

He said labor costs, as well as the need to replace equipment, have necessitated the increase.

"Thirty-eight cents was too low to begin with," Hinman said, noting the level was set at 38 cents in 1986 based on guesses about what the system, using new high-tech equipment, would cost.

The 38-cent charge raises $1.4 million annually. The extra 12 cents will add about $490,000 to that.

Salt Lake County's 911 system is controlled by three separate entities - a Valley Emergency Communications Center, which covers most of the valley; and separate centers in Salt Lake City and South Salt Lake.

The trustees of the valley communication center already have voted to raise the fees. The others have not yet.

Hinman met Thursday with mayors from throughout the valley, asking them to support the increase. Although the valley center can raise the fees without support from the cities, "We'd like the cities to endorse the plan first," Hinman said.