The Fairfax County Police Department, noting that its officers are increasingly at a disadvantage against armed suspects, has become the last major law-enforcement agency in the Washington area to sanction the use of semiautomatic handguns.

However, the transition from revolvers to 9mm semiautomatic pistols will be strictly voluntary, police officials said. Because the county has no money to pay for the new weapons, they said, those officers who want more firepower will have to pay for it. The cost of the pistols is $400 to $600.

Montgomery and Prince William county police also use 9mm handguns, but must buy them themselves. Most other local law-enforcement agencies pay for semiautomatic weapons in place of the standard .38-caliber police revolvers.

Like other police unions, the Fairfax Coalition of Police said the police department's more than 900 officers should not have to pay for tools to do their job.

"Nine millimeters are necessary in this era of crime," J.D. Fowler, president of Local 5000, said yesterday. "But we feel they should be provided by the department."

Maj. E. Thomas Sines said the police department agrees. But he added that the reality is that the county's budget squeeze is so tight, the department feared losing manpower to gain firepower. The county faces revenue shortfalls that already have necessitated more than $10 million in program cuts this year.

Sines, commander of the police department's Operations Support Bureau, said an informal survey of its officers indicated that more than 60 percent said they would be willing to buy the guns.

At Monday's county board meeting, Vice Chairman Martha V. Pennino (D-Centreville) asked county officials to review their figures to determine if money can be found for the weapons.

"I want our police to be as well-equipped as the bad guys," said Pennino, who added that she thinks finding the money is unlikely.

"The officer has to have confidence in his equipment," Sines said. "What happened is because everyone else went to the 9mm pistol, it put our people at a psychological disadvantage."

Although a Fairfax police officer has never been killed by gunfire in the department's more than 50-year history, the potential for harm is increasing, Sines said.

A review of search warrants obtained by investigators showed that semiautomatic weapons were seized in 60 percent of drug cases, not including those handled by officers on routine patrol, Sines said.

Sines said 9mm pistols are preferable to the standard service revolvers primarily because they fire more rounds. An officer can fire only six rounds with a revolver, and 15 to 19 with a 9mm handgun, he said. Further, he said, the semiautomatic does not have to be lowered for reloading, making it easier to keep an eye on a suspect.

While the department has chosen the 9mm as the standard weapon, it has not yet selected the manufacturer, Sines said. A group of 12 patrol officers from the county's seven police districts will test about a dozen models from Feb. 19 to March 1, he said.

According to a memo from Police Chief John E. Granfield to Richard A. King, the acting county executive, training could begin as early as May 6 and will include an initial 40-hour course followed by several four-hour reviews.