The final segment of a 243-mile, high-voltage power line ringing the Baltimore-Washington area is scheduled to come on line in 1994 now that Maryland's highest court has put to rest a 14-year battle over its construction.

Officials from Howard and Montgomery counties had tried to stop construction of the 10.5-mile segment by using their local zoning powers. But Robert C. Murphy, chief judge of the Maryland Court of Appeals, wrote in an opinion issued Friday that only the state's Public Service Commission can regulate statewide public utilities.

"A local governing body that has the power to altogether exclude from its jurisdiction a transmission line which provides electrical service statewide is essentially regulating the public utility in a manner that may be antithetical to the interests of the rest of the state," Murphy wrote. The Maryland legislature "could not possibly have intended this result."

The 500,000-volt transmission line is a joint project of the Potomac Electric Power Co., Baltimore Gas & Electric Co. and Virginia Power. It is intended to allow the utilities to exchange power among themselves and reduce the chance of power outages. About 200 miles of the line are in service now.

Pepco officials said yesterday they have begun condemnation proceedings with seven land owners, including the Howard County government, to secure a 150-foot-wide right-of-way for the remaining segment.

The last segment will snake through parkland, farms and residential subdivisions between Howard County's High Ridge substation in Scaggsville and the Brighton substation in northern Montgomery County near Brookeville.

The state Public Service Commission granted Pepco's request to build the line in 1980 over complaints dating as far back as 1976 that the line would damage property values, threaten residents' health and hurt the environment.

In 1987, the Montgomery County Board of Zoning Appeals also approved Pepco's request to build the line, but on the condition that the state Public Service Commission determine that it would not endanger the health and safety of people living nearby.

A year later, the Howard County Board of Appeals rejected Pepco's request, arguing that the utility failed to prove the line would not have "a detrimental effect" on neighborhoods.

However, the Maryland appeals court let the Public Service Commission's decision stand, ruling that the commission "is entitled to recognize the broader public interest of providing safe and reliable electrical service to larger areas" as long as it takes community concerns into consideration.

"There's not a lot we can do now," said Howard County Solicitor Barbara Cook. "The ruling was pretty definitive."

Staff writer Lisa Leff contributed to this report.