They were always well dressed and drove expensive cars, coming and going seven days a week from the discreet shopping center office advertised on the shingle outside as "Dean International Investments Inc."

"And everybody had a suitcase," recalled Barbara Martini, 33, a cosmetologist who is part owner of a manicure and makeup studio two doors down.

"They" were the alleged drug runner and money couriers who have been charged with funneling $19 million through a fake laundering operation. The operation was set up by federal agents, who posed as high-living criminals to infiltrate what the Drug Enforcement Administration said were several major narcotics rings. The undercover investigation lasted 18 months.

A federal grand jury indicted 67 U.S. and Colombian citizens, setting off a major sweep Friday that netted 36 suspects, 110 kilograms of cocaine and more than $800,000 in 12 Miami area bank accounts. The take made the sting, "Operation Swordfish," one of the hardest hitting attacks on south Florida's flourishing drug trade.

At the center was a group of DEA undercover operatives, some of them Hispanics, who acted as high-rolling money launderers. They worked from a plush-carpeted office suite with rented Cadillacs parked outside, a well-stocked liquor cabinet, a chest-high safe and a high-speed money-counting machine.

Their offices also were equipped, discreetly, with video cameras and tape machines to record what was going on.

For months the agents did business from the office, in a tree-shaded shopping center in the northwest Miami Lakes area, drawing the alleged drug smugglers more deeply into the charade with "seed money" from the Federal Reserve Bank. The cash went to buy cocaine and fund bank accounts created to give the appearance of large-scale money activity.

By April, the agents had moved to a bigger and still more luxurious office suite two miles away, adding to the impression of big-time dealing.

"But at night, they stole away to their homes, their working-class homes," said DEA spokesman Brent Eaton today as he reconstructed the sting.

The most difficult part of the investigation was luring the first few customers into the fake operation, he said. Agents at first relied on informers inside the drug underworld, Eaton said. But once Dean International Investments Inc. became known within a group of drug smugglers it generated its own business.

"It takes terrific informants to get people to introduce people to you," he added. "Once they got the first pickle out of the jar, things got easier. People came to them."

Another difficult step was knowing when to stop, whether the risk of blowing the cover was worth whatever additional evidence could be accumulated. In a sense, that decision was made for the agents, Eaton said, because they had arranged to buy 60 kilograms of cocaine for which payment was due Friday, more than $3 million at going wholesale rates.

"They had to do something by yesterday," Eaton said. "If you don't pay the money, or do something else, you're in big trouble."

The something else was Friday's series of arrests, the culmination of 18 months of expensive, dangerous work. The climax included some frustrations for DEA agents here, however.

First, Attorney General William French Smith announced the indictments and plans to sweep Miami for suspects more than an hour before the sweep had begun. Some agents grumbled that the early disclosure, beamed here instantaneously in radio newscasts, could have endangered lives by giving armed drug runners time to react. But no gunplay was reported.

One set of alleged cocaine merchants telephoned undercover agents at the Dean offices as the morning wore on, asking if they had heard the news of a big drug bust under way. The agents replied that all was well. Soon afterward, the accused drug smugglers dropped by with 11 kilograms, and were arrested on the spot.

At least one of the investigation's major targets, Marlene Navarro, 33, escaped arrest. Agents said Navarro, a Colombian living here, left town about two weeks ago and has been monitored in Colombia, the source of most Miami-bound cocaine.

It was not known whether she got wind of the sting or simply traveled to Colombia on one of her frequent business trips there.

Navarro was charged in one of the 67 indictments unsealed Friday with being the ring leader of a major cocaine smuggling and money-laundering operation that was duped into laundering more than $6 million in a dozen transactions with the DEA's dummy service.

"They would have preferred to wait until she got back, but they just had to go," Eaton said.

There was some satisfaction, however, in knowledge that Navarro's interest in a 42-unit South Miami condominium complex was seized, along with other suspects' cars, land and two homes worth half a million dollars.

DEA officials also expressed disappointment today that most of the 36 arrested have been freed on bond, many during an eight-hour hearing that wound up about 2:30 this morning. Agents complained privately that U.S. Magistrate Peter Nimkoff set bonds below levels considered effective by inflated Miami standards.