NEW YORK (AP) _ A police dragnet today sought the supplier of a deadly combination of heroin laced with a powerful tranquilizer that killed 12 people over the weekend.

Police in Connecticut, New York and New Jersey cruised drug-plagued neighborhoods Sunday to warn heroin addicts by loudspeaker to avoid ''Tango and Cash'' - the brand name marked on packages of the lethal narcotic.

They told people to seek medical help immediately if they had taken the drug, but as word of the danger spread police said at least one dealer simply changed the name and continued to sell it.

Police said that man was arrested, as were three alleged dealers in New Jersey, but that so far, none of those arrested appeared to be high-level dealers.

Officer Scott Bloch, a city police spokesman, said the drug was first sold Friday in an area of the Bronx known as a drug bazaar and magnet for out-of- state buyers.

Five people have died in New York, five in New Jersey and two in Connecticut since Friday. More than 100 people were taken to hospitals in the tri-state area.

Authorities said preliminary tests show the heroin contained a type of fentanyl, a powerful tranquilizer used in surgery. Underground chemists use it seeking to create synthetic heroin.

City Health Commissioner Woodrow Myers said preliminary tests indicated the heroin was laced with methyl fentanyl, which makes heroin 27 times more potent.

Myers said the drug induces a ''coma or respiratory arrest.''

Fentanyl and its variants have been blamed for more than 100 overdose deaths in the United States during the 1980s.

Detective Daniel Collins of Newark, N.J., said the publicity apparently led at least one alleged dealer, identified as Michael Johnson, 33, of Newark, to change the name on packages of the drug to ''Goodfellow.''

He was arrested for possession and sale of narcotics after police interviewed overdose victims.