WASHINGTON (AP) _ To improve emergency communications, federal regulators have earmarked additional slices of the airwaves for use by fire, police, rescue and other public safety groups.

The Federal Communications Commission, carrying out Congress' instructions in the Balanced Budget Act of 1997, announced Tuesday that is has made unused slices of airwaves available to public safety. The airwaves originally had been reserved for TV broadcasters.

The additional channels should greatly help, but may not solve, a problem public safety agencies have had for years: emergency communications systems that cannot talk to one another.

For example, in the 1993 bombing of the World Trade Center, a police officer could not talk to a firefighter just one level up on the 99th floor even though both had mobile phones.

Public safety groups and the Justice Department have complained that incompatible communications systems can hamper rescues.

The additional channels also should help public safety agencies in urban areas, where frequencies are congested.

The FCC voted on it Dec. 31.