Sam Duncam, who is 37, heads north on 14th Street, driving a black 1975 LTD that is also a Capitol Cab. He wears a denim tennis hat, a moustache and a leather jacket. He's a big an ex-Marine boxing champion. He has this big cottony laugh, like a baritone baby, when he talks about being scared.

"I work both calls and bumping the curb," he says. "When you hack for a living you can't be so choicy about where you're going, who you pick up, I've only got stuck up once."

Last week, two more taxi drivers got killed - one knifed, one shot. They're Nos. 4 and 5 who are dead this year and there have been 47 cab drivers robbed.

"I picked up two youngsters at 14th and park," Duncan says. "They give me an address that didn't exit. We rode up a few blocks, and they said pull into this alley, and there was this gun sticking in the side of my head. And what do you do but give it up?"

Duncan laughs; you know, what the hell, life's always coming back at you a little harder than you expect.

"They took my watch . . . they took my cab. I had to walk down to 14th backing for maybe a year then. Now I'm a little more cautious."

Duncan will drive another four hours till midnight. Right now he's turning up off 14th Street to a motel where he's got a call, if he can get through the kids leaping around all spidery in the headlights and some guy gunning a half-dead station wagon the pumps the street full of smoke.

"Most likely be a young lady waiting for us," Duncan says.

She ambles, cute and sly, down the steps in her black nylon blouse and her Pocahontas wig.

"Thomas Circle?" Duncan saks, and they both laugh. She won't tip, most likely, but prostitutes aren't dangerous, either. What you watch out for is two young black men. Or even one, like the one waving from the curb at 14th and T. Duncan pulls over.

"Where you doing?"

You can't understand the answer; the guy's drunk.

"You say Pierce Street?"

"I didn't say," the drunk says.

"Where you going, then?"

"Penn Street, Northeast."

"Get on in."

Dead yellow crime lights lurch through the cab. It's a nowhere Washington evening, September, end of the summer and end of the month, so nobody's got money. The prostitute gets out, leaving the drunk.

"You need the money," Duncan says, "you'll pick up most anybody. There been times I knew I was gonna get it. Some guy in back with sun-shades over his eyes and looking slick, and not saying a word.

"And he knew I knew.You can call in a signal 13 on the radio. But look at it this way. If you gonna rob me and I get on the mike. What are you gonna do? Hurry up and do it, that's right. Can you imagine? You're gonna rob me and I . . ." He laughs.

"They talk about those plastic shields across the back seat, but I hear - I don't know, but I hear - that up in New York they're found drivers with butcher knives in their backs, stabbed them right through the seat. A woman I know, she says, 'Why don't you carry a gun?' I told her you could have a Thompson submachine gun but all he needs is a 22, once he's got it up to your head."

The drunk pays, no tip and gets out at Penn Street.

"Let me show you some places," Duncan says. He heads for Anacostia and fires up another Kool.

"All of it's not real sweet," he says. "You figure, a man's got to be pretty dumb to rob a cab driver. What's he get, $30? If I had much more than that in my pocket, I wouldn't be driving."

Duncan slides off the freeway onto Martin Luther King Avenue, up past Big K. Liquors to Morris Road. He turns left, up the hills, big LTD tires thundering through the potholes, the trash and the dust.

"Lot of drivers don't like to come over here in the daytime, much less the night. That's why the driver always asks you where you're going. Now, the radio gives you some protection, but they don't tell you where you're going till after you bid on the call. Otherwise, nobody'd bid on it if you were going someplace like this. This here is Douglass Heights. It's awful hard to be getting a cab to Douglass Heights. I'll show you some places here that are beautiful; they're marvelous. . ."

Duncan laughs again and swerves the LTD into a parking lot behind an apartment house. Three young men lean against a van and watch the cab, moving their heads without moving their eyes, like lizards.

Suddenly, there's nothing but wall and cars on three sides, a rusted-out Flat with the wheels missing, broken glass leering back at the headlights, two-story brick project housing that always reminds you of February. You want to get out Duncan is laughing.

"Isn't this absolutely marvelous? Can you think of a better place for a stick-up? There's thousands of these little holes all over Southeast. I can laugh now, but it's not too funny when there's a guy in back who keeps telling you, 'Up in there,' and you don't want to go.

"You're out here by yourself, don't forget. It gets lonely; it gets bad. I'm the friendly kind, but sometimes when they don't talk, and you know they don't have any money . . ."

Sometimes, riding through the broken-brick stuttery glare of Washington at night, you can begin to understand the time-bomb loneliness and rage of the driver in Martin Scorsese's urban film-noir, "Taxi Driver."

"We're eight blocks from where they shot that driver last week," Duncan says, and then he tells you about the time the woman took off all her clothes in his front seat, and the drunks who can't remember where they're going, and he's laughing his big cosmic chuckle.

There's no way Sam Duncan could know that four blocks away from one of sih Southeast destinations on this night, Liberty Cab's Steven Adams would be shot in the head; or that yesterday, with Adams recovering in the hospital, two young men, Anthony Rush Bigelow, 19, and Marquette Henderson, 19, would be arrested in connection with the shooting.

But he wouldn't be surprised.