NEW YORK (AP) _ The crackdown on crack prompted the first blockade of New York Harbor since the War of 1812, but federal agents who halted scores of vessels recovered no illegal drugs and made just one unrelated arrest, a spokesman said Friday.

''I can tell you, anyone trying to bring drugs into New York will be arrested,'' said Coast Guard Capt. Arthur Henn, who headed Operation Glass Eye. ''We're out to catch those people bringing drugs into the port and poisoning our children.''

But the blockade produced just one suspect from the first 90 ships boarded. Thomas Hall, 27, of Asbury Park, N.J., was arrested when a computer check turned up an outstanding warrant for armed robbery.

Despite 45-minute stem-to-stern searches of 80 pleasure boats and 10 commercial craft, no drugs were recovered. The Coast Guard ordered one recreational boat to end its voyage because of safety violations, said Loren Bullard, a Coast Guard spokesman.

In two years, the Coast Guard has made only five drug-related arrests in the New York harbor, said Bullard.

Mayor Edward I. Koch blamed publicity for the lack of results.

The search ''wasn't a very well kept secret on the part of the Coast Guard, because everybody I met Thursday told me about it,'' Koch said. ''That's no way to run an operation. That's got to be done very quietly.''

Bullard said the blockade was merely the start of intensified efforts to stop drugs from coming into the harbor. He said random searches and blockades would occur in the future.

''The primary focus of this operation is to let people know that we're going to be out there looking for them and they won't know where or when,'' he said. ''We may not get you tomorrow, but we're going to get you.''

Fifteen Coast Guard boats and cutters, joined by four city police boats and two from U.S. Customs, stopped each boat as it entered the harbor through the Verrazao Narrows between the boroughs of Staten Island and Brooklyn. Searches were conducted at Coast Guard piers on Staten Island.

The program started about 8:45 p.m. Thursday, and was ended at 5:12 p.m. Friday when more than 200 law enforcement officials came in off the water, said Petty Officer James Graham.

Henn, calling every craft that enters the harbor a potential smuggler, said the program was sending a message to drug runners.

''On a day-to-day basis, Coast Guard boats are out in the harbor making random boardings,'' Henn said. ''So people never know when they'll be stopped.''

Hall was arrested aboard the fishing vessel Savage, which ignored signals to steer to the pier. The 75-foot boat ran aground as a Coast Guard cutter headed toward it and had to be brought in by a tugboat, said Petty Officer Richard Schnurr, a Coast Guard spokesman.

The harbor blockade, the first since the British blocked off the waters in 1815, was the latest effort in the city's battle against drugs, particularly crack, the highly potent, inexpensive cocaine derivative.

On Thursday, police teams went through 200 retail outlets and seized 40,000 crack pipes, and prosecutors announced the establishment of a special ''crack court,'' created to handle only cases involving the drug.

Police also have begun seizing the cars of out-of-state drug buyers who drive into the city to make their purchases.

Bullard said Operation Glass Eye had been kept ''under wraps'' but he expected other cities would follow the lead.