A 15-mile-long police chase through the Gaithersburg area at speeds of more than 100 miles an hour ended early yesterday when a fleeing car carrying three men crashed head-on into a police cruiser, injuring a Montgomery County officer, police officials said.

Officer Earl Brown, who is assigned to the Germantown station, was treated at Suburban Hospital for unspecified injuries and released, officials said. The three men in the speeding car, who were arrested on assault and drug charges, were treated for apparently minor injuries at Shady Grove Adventist Hospital and released, police said.

The chase began shortly after 3 a.m. when two off-duty county policemen saw a car heading north "erratically" on I-270 near Montgomery Mall, officials said. When the officers attempted to stop the car, it sped away, and, as other cruisers joined the chase, the fleeing car was clocked at more than 100 mph.

Occupants of the car tossed beer bottles and cans at pursuing cruisers, police said, along with "a plastic bag containing a leafy green substance." The fleeing car turned east off I-270 onto Rte. 118, sped to Rte. 355 and headed south to Quince Orchard Road. At the I-270 overpass, the car crossed the median and crashed into Brown's cruiser, police said.

Police arrested three men identified as Victor A. Cabaral, 26, of 5225 Pooks Hill Rd. in Bethesda, Anthony G. Eckstein, 24, of 7604 Marion St. in Forestville, and Thomas J. King, 20, of 3910 Bowie Mill Rd. in Olney.

All three were charged with assault with intent to murder, possession with intent to distribute PCP and conspiracy to distribute PCP. In addition, Cabaral was charged with driving under the influence.