Hundreds of antinuclear protesters repeatedly assaulted the Seabrook atomic power plant yesterday but were repulsed by state troopers and National Guardsmen using fire hoses, Mace and a smoke-spewing generator.

Waves of demonstrators twice assaulted the fence surrounding the construction site and tore down sections of it in attempts to take over the facility.

More than 1,000 demonstrators then massed at the plant's main gate, where helmeted troopers and guardsmen turned fire hoses on them and a stream of smoke from a generator.

Several people were taken into custody, and police confiscated gas masks and other paraphernalia.

Earlier, a squad of 25 helmeted troopers confronted about 75 protesters as they built a pontoon bridge across a tidal inlet in the marshland.

Troopers sprayed the demonstrators with Mace and tossed crowd-control canisters while two boat crews of state fish-and-game officers used jackknives to slash truck-tire inner tubes supporting the bridge.

The governor's office first said the police used tear gas, but later said it was only smoke.

Some demonstrators stood in three feet of water, unsuccessfully trying to block the police from sinking the bridge. Others scurried to high ground.

Having camped overnight in the rain, some demonstrators vowed to stay until at least Tuesday. Those departing said the takeover force was too small and not well organized.

The demonstration by the Coalition for Direct Action at Seabrook was the first attempt to occupy the plant, a rallying point for nuclear protests since construction began in 1976. The coalition is a militant offshoot of the Clamshell Alliance, organizer of several peaceful protests at the site.