CHICAGO (AP) _ This city has been a pace-setter in crime since the machine-gun days of Al Capone and John Dillinger, but so far it has oddly missed out on crack, the devastating new form of cocaine.

The crystalline or granular form of the narcotic, available in small doses at bargain-basement prices, is wreaking havoc in New York, Los Angeles, Miami, Detroit and other cities.

But not in Chicago.

''Cocaine, without a doubt, is our No. 1 priority. Seventy-five percent of our cases in the last fiscal year were cocaine-related,'' said spokesman Fran Hirzy at the local office of the U.S. Drug Enforcement Administration.

''But crack - it's not here.''

Commander John R. Ryle of the Police Department's narcotics division agrees.

''We've not been able to purchase any or even raid a crack house. Certainly it's unusual,'' Ryle said.

Theories abound as to why a city flush with contraband has so far escaped one of the nation's biggest urban nightmares.

''Perhaps it's the adverse publicity about what this stuff can do to you. It's the most dangerous addiction on the street,'' Hirzy said.

And the gangs who control much of the city's drug trafficking can be curiously conservative, said sociologist Hugh Horan at the University of Illinois-Chicago school of public health.

They may simply not want to diversify from cocaine in powder form, Horan said.

On the West Side, police Sgt. Gene Connelly of the gang-narcotics unit deals with the notorious Vice Lords gang, whose members number in the thousands.

Their primary enterprise is peddling narcotics, mostly cocaine. But not crack.

''From January 1 to May 1, we conducted 566 raids. We have yet to come across crack,'' Connelly said. ''For the year of 1987, we had 1,628 raids and did not come across it.

''You'd think somehow out of all the raids, either with a search warrant on a house or a simple stop on the street, we'd find it. But we haven't come up with one piece of crack.

''I talk to cops with other towns and they think it's coming from here. I tell them, 'We ain't got it.'''

City gangs are involved in street sales of marijuana, cocaine, PCP and heroin, but Ryle said crack makes up ''maybe less than 1 percent of all cocaine received by the police department.''

Crack has appeared on U.S. police blotters since 1981, according to the DEA.

Popular in the inner cities because it can be bought in small quantities for as little as $5, crack is smoked and can take effect in 10 seconds - much faster than cocaine in powder form, which is snorted.

But a 22-page DEA internal report on crack, published earlier this year, said of Chicago:

''No cases are currently under investigation or being developed ... as no serious crack problem exists in this city.''

U.S. Attorney Anton Valukas says the lull may be temporary, noting that cocaine ports like New York, Miami and Los Angeles are flooded with the drug.

''And when something like this hits the coasts, we usually follow the trend,'' Valukas said.

But crack already is a problem of staggering proportions in another Midwest city. Detroit, a long way from either ocean, has an estimated 1,000 crack houses.

Illegal drugs are readily available here in the nation's third-largest city, a transportation hub and key distribution point for goods of all kinds.

In February, federal agents at O'Hare International Airport found 165 pounds of heroin worth $1.8 billion hidden in religious statues from Thailand.

On May 24, police and federal drug agents confiscated 247 pounds of brown heroin - the largest single seizure in U.S. history.

Last July, Attorney General Edwin Meese III told reporters the government had seized 2 1/2 tons of cocaine at a fruit market after tracking it from Florida.