NEW YORK -- A call crackles in over the Emergency Medical Service radio: cardiac-arrest case in Greenwich Village. Brian Dennis, an EMS supervisor, flicks on the siren and flashing red light and begins weaving his patrol van through the obstacle course of lower Manhattan.

Rounding one corner, Dennis stops abruptly to avoid hitting a man wearing headphones and sauntering across the street. At Greenwich and Barrow streets, a bus pulls from the curb and pins his vehicle next to a maroon car. One block later, he is stuck behind a cab.

By the time Dennis arrives, the patient is dead. The victim was seriously ill with AIDS, but a few minutes might have made a difference this time.

Exasperated, drumming his fingers on the steering wheel, Dennis blurted, "The siren is supposed to be effective, but people just ignore it."

Riding one shift with a paramedic is enough to demonstrate a fresh fact of life in New York: A remarkable number of motorists and pedestrians do not make way for blaring sirens and flashing red lights. Paramedics, firefighters and police officers say the problem is becoming worse, preventing them from responding to emergencies and jeopardizing the lives of people who need help.

Officials at city agencies said they do not keep statistics on the number of such incidents but reported hearing an increasing number of complaints from drivers of emergency vehicles.

The most common complaints involve novice cabbies and uncooperative truckers, but also cited are some of New York City's lesser-known nuisances -- itinerant windshield washers, bumper-tagging bicycle messengers and preoccupied pedestrians.

"Every day, it gets worse," said firefighter Paul Hashagen of Rescue Company No. 1 in midtown. "I started driving fire trucks 12 years ago, and you had a few people that might not yield the right of way. Now it seems that a good percentage of people don't yield, including people that used to be courteous, like bus drivers and cab drivers."

Part of the problem, some emergency workers agreed, involves the "boy who cried wolf" syndrome. Manhattan's concrete canyons constantly reverberate with alarms, some of them false, and many people here have simply come to disregard all sirens.

"There's always some type of emergency going on in New York City," said Sean Moogan, a medical technician at the EMS, which received more than 1 million emergency calls last year. "People are so used to hearing sirens that they don't pay attention to it. They think what they're doing is more important. That's fine unless you've got a 'difficult-breathing' child on board and you've got to get to a hospital."

Many motorists are obstinate. Last Monday, the driver of an oil truck refused to move his vehicle, which was blocking a narrow Upper East Side crosstown street, despite the pleas of an ambulance crew carrying a heart-attack victim. The ambulance driver had to back up and go around the block.

Paramedics and firefighters alike cited cabbies as the worst violators of the law that says motorists must pull to the side of the road when an emergency vehicle approaches.

Some cabbies seem confused about what to do, they said. Others tail fire trucks or ambulances, driving in a vehicle's wake to cut through traffic.

"At least once a week, there's a cab-and-ambulance accident in the city," EMS Lt. Tony Torres said. "Some cab is going to drive behind you, but he doesn't know when you're going to stop."

Another technique used by cabbies is driving directly in front of ambulances, which exasperates EMS drivers. "See that bar over here?" Moogan said, pointing to a checkerboard-patterned pin above the other EMS medals on his chest. "That's for the taxi I killed." He added quickly, "Just kidding."

But the level of frustration is high and many emergency workers blamed the problem on the city's shifting ethnic composition.

"It's just a new breed of people driving cabs now," Hashagen said. "Maybe in the countries they're from they're not used to so many emergency vehicles. It used to be all Irish and Jewish cab drivers in New York, but now the drivers just nod and smile and cut you off. They just don't understand your mission."

Failing to yield to an emergency vehicle carries a $100 fine, but officials say it is very difficult to enforce.

"The violators are moving and the majority of our agents are on foot," said Joseph DePlasco, a Department of Transportation spokesman. "People feel they can get away with things here that they wouldn't try somewhere else. New York is probably the only place in the world where a stop sign is seen as a suggestion."

Statistics show that EMS response times are improving and that many ambulances reach their destinations unimpeded. But drivers said they encounter at least one unnecessary delay each day, even though they know to avoid certain points of chronic congestion. These include the Garment District, clogged with delivery trucks, Broadway's Theater District during Wednesday matinees and Rockefeller Center during Christmas season.

Emergency drivers who whiz through narrow labyrinths at high speeds must be on the lookout for other peculiarities of street life here. They talk of thrill-seeking bicycle messengers who hang onto their bumpers and of windshield washers who slather vehicles at red lights and refuse to move aside until they have been paid.

Even police officers said they do not always get the consideration they expect. "We have 'POLICE' written on the front of our truck and the drivers still don't pull over," said one transit officer who asked not to be identified. "One guy we stopped recently and cited told us, 'I would've stopped if I had known you were cops. I didn't pull over because I thought you were an ambulance.' "