The mayor says he feels sick at heart. The police chief says his officers were caught off guard. And with tear gas blowing in the soggy wind off Puget Sound, it is clear that nine meticulous months of security planning for the global trade talks underway here have gone, literally, up in smoke.

In the grip of protests that are larger and at times rowdier than they say they anticipated, city officials conceded today that their tactics in dealing with the impassioned crowds of labor, consumer and environmental activists who began swarming downtown Tuesday should have been different.

"Clearly, in hindsight the approach we adopted yesterday did not work," Assistant Police Chief Ed Joyner said at a news conference this morning.

That somber assessment came just hours after Seattle had imposed its first dusk-to-dawn curfew since World War II and dispatched several hundred unarmed national guardsmen to help police in riot gear contain the demonstrations, which have closed and damaged businesses here and succeeded in disrupting the World Trade Organization's conference.

After dousing groups of protesters Tuesday with tear gas and pepper spray, and even firing rubber bullets at some of them, police officials today created a 50-block no-protest zone around the conference site, sealing much of downtown from the public.

Some residents, irritated by the turmoil, welcomed the crackdown. Ron Cowan, a Seattle native, said demonstrators "must have something better to do today. . . . They are not accomplishing anything but breaking windows and making a mess."

By late afternoon police had arrested more than 400 demonstrators who had entered the zone. But this city's leaders still sounded quite shaken.

"I'm very distressed to see videos of our beautiful city with tear gas and police dressed in riot gear," Mayor Paul Schell told reporters. ". . . The last thing I want to do is be mayor of a city where I had to call the National Guard. . . . It makes me sick."

City officials had been working closely since early this year with leaders of the diverse protest movement that has engulfed Seattle. Police officers had been trained specifically for the gathering, one of the largest international events the city has ever hosted--and one with a history of drawing violent protests. The last time the WTO met at its headquarters in Geneva, protesters overturned cars and set them on fire.

The officials said they had been assured that the demonstrations would be peaceful and choreographed, to the point that they had even agreed in advance to wait until protest cameras were rolling to make some mass arrests. But some protest organizers said they had warned the city of trouble from fringe groups.

Some critics said Seattle authorities seemed to be naive in preparing for such a large event.

Former D.C. police chief Isaac Fulwood Jr., who supervised security for dozens of major demonstrations in the nation's capital, said today that Seattle's law enforcement officials did not plan enough for the worst-case scenario.

"Whenever you have a demonstration of that magnitude with the president and world leaders coming, you can't take anyone's word on face value," Fulwood said. "You have to plan for the worst all the time. And you have to have an intelligence operation that's pretty major."

But Seattle officials adamantly defended their conduct in preparation for the protests and praised how disciplined many officers have been on the streets under tense circumstances.

"Based on the threat analysis, quite frankly we didn't have any reason to believe they would engage in this behavior," Joyner said. And Police Chief Norm Stamper called many of his street officers "heroic."

"The distinction between lawful protesters who had a message that they wanted to deliver and those who had a different message that they wanted to deliver is, in fact, very clear to us," Stamper said.

But some protest leaders and local residents are accusing police of firing tear gas and other crowd-dispersing weapons on demonstrators who have been peacefully exercising their rights to free speech.

Erika VanNyatten, an employee at a company in downtown's Ranier Tower, described the scene as chaotic and said that officers seemed to be using excessive force. She also complained about the moratorium on protesting. "Protesters have a legitimate right to protest," she said.

Staff writer Sari Horwitz in Washington and special correspondent Khiota Therrien in Seattle contributed to this report.

CAPTION: Above, a handcuffed protester winces as she is carried away and detained by police in Seattle. Police arrested more than 400 people yesterday. At left, weary officers lean on each other for support while resting.