Montgomery County police said they unexpectedly seized about $400,000 worth of cocaine Tuesday night after an alleged dealer took them by surprise, offering to sell 2 kilograms of the drug to an undercover officer during an initial get-acquainted meeting.

"It isn't always this easy," Lt. Ronald Ricucci, head of the Special Investigations Division, said at a news conference yesterday. He said dealers who traffic in wholesale amounts of cocaine sometimes meet with buyers several times before feeling comfortable enough to make a sale.

Narcotics officers thought this get-acquainted process was only beginning when Domingo Martinez, 32, of Bowie and an undercover officer met for the first time about 6:30 p.m. Tuesday in a restaurant parking lot at Rosedale and Wisconsin avenues near downtown Bethesda, Ricucci said.

But within an hour, he said, Martinez and his alleged partner, James F. Greene Jr., 36, of Kensington, were under arrest and detectives had made what Ricucci said was the department's third large cocaine seizure in nine months. Describing the cocaine as "nearly pure," he said that once the 2 kilograms had been diluted and parceled as ounces and grams, it would have brought about $400,000 in sales to users.

The seizure comes as police have noted a marked increase in the availability of cocaine in the county, Ricucci said. In December, they seized 3 kilograms and made four arrests in Colesville, and in March they arrested 12 people and confiscated 15 kilograms in Chevy Chase in the largest cocaine seizure in county history, he said.

Ricucci described Martinez as "a major" supplier of cocaine to street-level dealers in the Bethesda-Chevy Chase area.

After arranging by telephone to meet Martinez, the undercover officer drove to the parking lot with $40,000 in a briefcase, money lent the department by the U.S. Drug Enforcement Administration, Ricucci said. He said the officer expected to show Martinez the money as a sign of good faith and to meet him again some night to discuss a transaction in more detail. As the officer waited for Martinez, Ricucci said, Greene allegedly cruised the area in a van, scouting for police.

Greene, who Ricucci said was being paid with cocaine for his night's work, failed to notice detectives who were watching the scene from about 10 unmarked cars around the intersection, Ricucci said.

Martinez arrived about 6:30 p.m. in a BMW, and after only 15 minutes of conversation, Ricucci said, he surprised the undercover officer by proposing to sell him 2 kilograms for $54,000. The officer replied that he had enough money in the briefcase, Ricucci said, and Martinez told him to drive about two miles to another parking lot at Wisconsin and Maple avenues.

While Martinez allegedly fetched the cocaine from an apartment he maintains at 7034 Strathmore Ave., Ricucci said, Greene drove the van to the second parking lot and again allegedly scouted for police officers, and again failed to notice the unmarked cars, which took up positions near the lot. When Martinez returned, the police made the arrest, Ricucci said.

Ricucci said police found a hunting knife, hatchet and meat cleaver in the van Greene was driving. Greene and Martinez, who was not armed, were charged with possessing cocaine with intent to sell and conspiring to sell cocaine. Each was being held last night in lieu of $1 million bond.