A third police officer and two other Brink's guards were wounded in the two exchanges of gunfire. More than a hundred state troopers, aided by helicopters, searched through the wooded area near Route 59 and the Thruway for the suspects, and roadblocks were placed on the Tappan Zee Bridge and major roadways.

The shooting stunned Nyack, a community of 8,000 about 25 miles north of Manhattan. When a police officer blocking the door of the two-story, red-brick police headquarters was asked the size of the department, he said, ''It was 22,'' emphasizing ''was.'' Then he shut the door.

Kenneth Gribetz, the Rockland County District Attorney, told a news conference at midnight that four of the robbers jumped out of a red van parked near an entrance to the huge two-story shopping complex and began shooting.

''They just opened fire on them,'' he said. ''It happened very fast,'' said Jack Horan, a security officer at the bank. The Brink's guards left the bank, he said, ''and the shooting started. People started shouting and we saw the van leaving.''

After a Brink's guard fired a single shot, the robbers drove off, abandoned their van in the parking lot of a Korvette's store on Route 59, and changed to two other vehicles, a yellow Honda and a rented van, Mr. Gribetz said.

The two police officers were killed a few minutes later when they stopped the van at the roadblock. ''As a detective was proceeding away from the back of the van,'' he said. ''individuals, believed to be three, jumped out and opened fire on the police officers.'