A hulking, Army-trained sharpshooter described as steeped in the Nazi philosophy of Adolf Hitler took over the warehouse where he worked today and killed five persons, including a policeman, then killed himself.

The climax to a day-long siege came about 6 p.m., when Fred Cowan, 34 a six-foot, 250-pound body-building enthusiast, was found with a bullet in his brain fired from his own handgun.

A law enforcement assault team found the body as it closed in on Cowan's second-floor stronghold in the Neptune Worldwide Moving Co. warehouse on the outskirts of this Westchester County community, 1 1/2 miles above the New York City line.

The last shot attributed to Cowan was heard about 2:30 p.m. No other shots were heard, but police did not attempt to move in on Cowan until 6 p.m. because they feared he was still alive and holding hostages. No hostages were found inside the building.

Five persons, including three police officers, were wounded.

Police said Cowan's apparent motive was revenge on a dispatcher who had suspended him for two weeks for being rude to a customer. This was his day to return to work, but when he arrived shortly before 8 a.m. he was carying an M-16 automatic rifle.

As many as 50 employees were due at the warehouse for that shift, but there was no immediate count of how many were inside when the shooting began.

Many of them remained inside at the mercy of Cowan, either as hostages or afraid to flee. But as the hours wore on, they ventured forth singly and in pairs to take their chances on reaching the safety of police lines.

One of these was Robbie Cohen, who hid for a time in a rest room. When he finally emerged from hiding, he said, he was ordered out of the building by Cowan.

"I figured that was my passport out of here," Cohen said late, "so I just took off."

Cohen said, "He's a quiet guy who came to work every morning. But he was too quiet. You got to watch those guys. They can erupt like a volcano at any time.

But others who knew Cowan sketched a more sinister portrait. One neighbor who declined to give his name said the gunman was a collector of Nazi uniforms, tattooed his body with Nazi symbols, and festooned the walls of his room at home with swastikas.

"He walks around in a Nazi uniform sometimes," the neighbor said. However, Cowan was reported merely as khaki-lad when he died.

Another neighbor, Roland Lersch, 20, said:

"He was always coming in with white-imperialist magazines. He hates blacks. He hates Jews."

"He's got every kind of a rifle that ever was made," the unidentified neighbor said. "And has been collecting them since he was a kid. Ever since he was a kid, he's been bugged on Hitler. Hitler is his idol."

In 17 months in the Army, including duty in West German, Cowan had twice been court-martialed - once for being absent without leave and once for leaving the scene of a highway accident. It was during this service that he acquired proficiency in weaponry.

"He just started shooting and everybody started running all over the place," said Clint Wynant, a warehouse employee.

Falling dead in the first onslaught inside the warehouse were Pariyaral Varhese of New Rochelle, a native of India; Joseph Hicks and James Green, both of nearby Mount Vernon, and a fourth man, not initially identified.

New Rochelle police arrived quickly at the scene, an industrial area of small commercial firms, gasoline stations and garages. One of the first, Allan McLeod, 29, was shot down as he rushed toward the warehouse entrance.

His body lay for several hours until police moving in behind a tank-like armored personnel carrier managed to retrive it.

Hour followed hour as the police force was augmented by FBI agents and by siege experts from the New York City police department. A two-square-block area was cordoned off as hundreds of the curious flocked to the scene.

Police sharpshooters took to adjacent roof tops and the armored car rumbled back and forth outside the two-story warehouse.

FBI agents slipped into the first floor of the warehouse without opposition and removed the four dead workers. Cowan had withdrawn to the greater security of the second floor.

At noon, Cowan telephoned out a request for something to eat. It was ignored. While he had established his own contact with the outside, the authorities were unable to make it a two-way circuit back to him.