The night of Sept. 13 started out like any other for John Clagett, a cab driver. He carried a government official, then a Spanish-speaking couple, and then an elderly man from the Soldiers & Airmens Home to a go-go club. The elderly man was drunk and obnoxious, but in Clagett's business you never know who you're picking up.

Shortly before midnight, two young black men flagged him down. They wanted to go to 2d and Parker Streets NE, and out-of-the-way place by the railroad tracks at Union Station.

He knew it was an odd place to visit at that time, but Clagett, 39, was an ex-social worker and didn't like to discriminate.

At 2d and Parker they put a gun to the back of his head.

"Gimme your money or we'll blow your head off," one of the young men said. The other leaned over the front seat and grabbed the keys.

It went down as an armed robbery, complaint no. 439898 in the files of the District of Columbia police department - one of nine cabbie holdups this month. One driver has been killed, three wounded and the other five threatened with knives, guns or other weapons.

Hackers have always been prey to street sharks, but the frequency of attacks recently has struck fear even in veteran cab drivers. Dispatchers say that cabbies will no longer go into Far Northeast or Southeast, and many drivers - both black and white - say they now avoid young black men.

Most of the holdups have occurred in Northeast or Southeast, and the suspects are said to be black youths. Most of the victims of the robberies have been black cab drivers.

"If they aren't middle-aged, I don't see 'em," said Walter Primis, who is 6 feet 4, and 270 pounds, and drives for Eastern.

"They can take my license away (for refusing to pick up a passenger), I don't care. I'd rather lay bricks than be dead," said Dan Gillespie, 32, who drives for Diamond.

Longtime observers of crime here report more tension among cab drivers now than at any time since six drivers were shot in a 10-day period about 25 years ago.

Mayor Walter E. Washington and Police Chief Maurice J. Cullinane have promised increased police patrols and possible installation in cabs of SOS devices.

Late yesterday, police announced the arrests of two 16-year-old youths on robbery charges and said they were seeking a third teen-ager, allegedly the triggerman, in the shooting of a taxi driver in Southeast last week.

Clagett, who has been driving a cab for three years, reacted instinctively when he was held up. "The money is right here in my pocket," he told two assailants at 2d and Parker Streets NE.

"Let's lock him in the trunk," Clagett said he heard the man with the gun say. "No let's make him take a walk," the other man said.

The one man couldn't get the car keys out, because Clagett had stopped in drive. Clagett passively moved the taxi into park so they could take his keys. The men told him to start walking, that they would shoot him if he turned around.

After walking about 50-yards, Clagett said, he looked and they were gone. He called the police from a pay phone.

"Is this a pattern . . . what can I do?" he asked the officers.

The officers crawled around the cab with their fingerprint powder and asked him to describe the men. Clagett said he hadn't gotten a good look.

"The police got a fingerprint off the gear shift, and said that was a positive ID, and I haven't heard from them since," Calgett said in an interview this week in his cab.

They took $50. Because of it, Clagett is now two weeks behind in his rent.

He recalled the details of the robbert without emotion. "You've got to expect it in this business," he said. "We got cash in our pockets and we're vulnerable. We're alone out here, you know what I mean?"

It's clear the incident has left mental scars. "I picked up two young guys the other day. They were going to Walter Reed. They worked there and we were talking all the way, but by the time we got there I was exhausted from the strain. When we stopped I could feel the skin crawling up the back of my neck."

Before the holdup, Clagett said, he would take anyone anywhere. He has lived in the predominantly black Mount Pleasant section of the city for a dozen years, and was sympathetic to young blacks who complained they had trouble hailing cabs. Now, Clagett says, he too, passes them by.

"The young people say, 'what's wrong with me . . . why can't I get a ride . . . we're being discriminated against," Clagett said. "They're right, they are being discriminated against. I'm doing it to be comfortable."

So Clagett, along with many of the other 11,000 cabbies in the city, now find themselves avoiding certain passengers and clinging to the downtown and Northwest areas and to streets with anticrime lights. These men who know every street and alley in the city seem as frightened and suspicious as people lost in a forest.

At 1 a.m. yesterday Jim Hoffman, a dispatcher for Eastern, had a pile of telephone request slips from people in remote areas of the city seeking taxis. Many of the slips had been in front of him for hours. "I got regular customers in Southeast and I can't get any drivers to go out there," he said. "A few weeks ago drivers would be jumping to get at these calls. Now when I put out the calls they just turn off their radios and go looking on their own."

Gillespie the Diamond driver was yoked with a chain by two young men in a holdup at a housing project in Southeast two years ago. Now he has stock answers to refuse fares. "I just tell 'em 'I'm not goin' that way, or 'I got to pick up my wife in 10 minutes," he said.

It's illegal to refuse to pick up someone who hails an empty cab, but the drivers say they don't care. "They can take my face (license) but I won't stop for blacks youth," said Primis, the burly Eastern driver who is black.

"I'm prejudiced, if you 18 or 19 years old," Primis said. "Even my children, if they weren't my children, I wouldn't pick 'em up." By picking up such fares, he said, "you stand a better chance of dyin.'"

Clagett, like the others, says he'll keep on driving. He can net $5 an hour, he says, and he likes the independence.

The threat of holdups, he says, appears to be something cab drivers will have to live with, like obnoxious passengers. "Cab drivers need to do something," he said, "but I'm not sure what."