A heavily armed gunman was holding two bank employees hostages ia Silver Spring branch of Citizens Bank and Trust Co. of Maryland last night, according to Montgomery County police.

The gunman, reported to be armed with two rifiles and 250 rounds of ammunition, had intially seized four hostages, but later freed two of them, a police spokesman said. The two hostages still being held at the bank branch in the Blair Park shopping center on East-West Highway at Colesville Road were believed to be women.

The gunman twice fired rifle bursts, once into the bank's ceiling and once through its back door, according to Cpl. Pilip Caswell, the police spokesman. No one was reported injured by the gunfire.

Negotiations with the gunman were taking place by telephone, police said. Shortly before 8 p.m. the man released a woman hostage in return for being given a bullhorn. "We're going to wait him out," the police spokesman said.

Reached by telephone by Washington Post staff writer Robert Meyers, the gunman said.

"The next time I hear some thump thumpies, I'm going to waste someone. I've already used three rounds (bullets) and I've got 250 more. That's an awful lot. I don't want to kill anyone. But the next person to come near that vent I'm going to shoot. If they don't stop coming around I could stop and think about what I want to do. Hey, what do you want - an exclusive or something? Well, I don't give no exclusives." Then he hung up.

In an earlier phone call from Meyers, a woman answered the phone, apparently crying. When she turned over the receiver to the gunman, he began by saying, "Love ya."

Dozens of armed Montgomery County police and FBI agents surrounded the bank in the small shopping center and cordoned off the area. The shopping center is on the fringe of the central Silver Spring business district a block from the District of Columbia line.

According to one report, two gunmen had originally entered the bank to attempt a holdup, but one escaped before police arrived. Police said they could not immediately confirm this report.

County police Officer Mark Smith said the robbery attempt was foiled when a bank employee apparently a teller, tripped a silent alarm, bringing police to the scene shortly after 6 p.m. The bank normally is open until 8 p.m.

According to the police spokesman's account, the gunman first detained six bank employees and several customers. He ordered the customers to leave. Two bank employees also got out with the customers, the spokesman said.

Later, the spokesman said, another bank employee a man, was allowed out the bank's rear door, leaving three hostages inside. Then the woman hostage was exchanged for the bullhorn.

Police described the gunman as 23 to 25 years old. They said he was slender, weighed about 150 pounds, had black hair and was dressed in a white shirt and a green, Army-style vest.

The identities of the suspect were not immediately made known.

Busineses in the shopping center were ordered to close shortly after police arrived. Alan Friedman, an employee of the High's Dairy Store nearby, said a detective tole him to lock his front door, turn out the lights and wait in the rear of his shop as a precaution against gunfire.