Saturday morning, at an hour so early that most of London wouldn't need any excuse to stay in bed, and so cold as to offer one anyway, Lynne and Trevor and David drive down a country road in a beat-up Ford that reeks of cleaning fluid. They've been at work since 6 a.m., pouring gallons of detergent over the lovely fields of Surrey, south of London, and stringing slow-starting explosives in the trees.

The powerful-smelling detergent is to confuse any hounds that may apprroach on the trail of a fox. If that doesn't work, the explosives should scare foxes away from the area. It is still hours before the weekend fox hunt begins at midmorning, but there is much more to do.

Lynne Chamberlain, 29, David Wilkes, 30, and Trevor Williams, 35, are hunt saboteurs, or "sabs" as they call themselves. They belong to a national organization claiming about 4,000 supporters in Britain, a radical splinter group of the more staid 50-year-old League Against Cruel Sports.

Now an almost invariable accompaniment to hunts all over Britain, the sabs try to save foxes, deer and otters from the gentry whenever possible, and to call attention to what they insist is a cruel sport. From 15 years of effort the animal lovers have reaped a handful of newsprint paragraphs, a few halfhearted attempts from the Labor Party to abolish hunting, several arrests and some broken bones.

Recently, a sab got his jaw broken in an argument with a hunt enthusiast in Southampton, in southeast England. That same day in Lancashire, in northern England, sabs shouted abuse at Prince Charles himself, an avid hunter, as he returned from a horse show.

"We got quite good coverage from both of those," says Williams. "But I've got no illusions that we'll be the ones to stop hunting. I see our role merely as keeping it in the public eye."

Williams, a lanky, mustachioed man who works at a laundry service, has been a sab for five years. He's been arrested twice, once for creating a nuisance at a hare-hunting exhibition, and once for exhuming the remains of a fox club after a hunt and placing them in the middle of a busy shopping center. Others have been arrested for breaking windows, chaining themselves to embassy walls and freeing animals from breeding centers and laboratories.

"A large number of sabs are actually anarchists," argues Richard Tracey, a spokesman for the British Sports Society. "They turn up at every sort of demo, whether it's against fox hunting or the troops in Northern Ireland. We don't think they're frightfully sincere, and they certainly don't have any respect for a tradition which goes back centuries."

The sabs hang around the fields throughout hunts, unwittingly conspicuous in their mock hunting attire. They get into arguments with redcoated hunting masters and shout epithets at the older members of the hunt, who often shout back. The sabs say that when they look at the pageantry of black-and-red riding coats and horses with braided manes mincing through farmland straight out of Thomas Hardy novels, they see it all only from the viewpoint of the fox, which faces a bloody death.

At the Saturday hunt in Surrey, the group, using their horns, successfully split some dogs from the pack. Once they did, they had to use all their strength to keep the frantic hounds away from the road and safe from passing cars. But they were scrupulous about it, bringing the dogs back in their old Ford to the hunting lodge.

"What bothers me most," David Wilkes, a laboratory assistant and a longtime sab, said of the hunters, "is that they hunt for pleasure. Perhaps it's an undeniable facet of human nature, as the hunters say, but it makes me sick. A lot of hunts still have this ceremony at the end, called "blooding,' where they take the fox's blood and smear it on the youngest member of the hunt. That's why I hate it, that they could reach kids like that."

"I'm 37 years old and I've never seen that ceremony," counters spokesman Tracey. "Of course, that doesn't mean it never happens. But it can't happen very much. And if it weren't for the hunt, foxes would be snared and poisoned and shot. That's really less humane, isn't it?"

Tracey says the sabs have had little or no effect on hunts, and are regarded as merely "minor irritants." The number of participants in all kinds of hunting sports is growing, he adds. "I'd say 300,000 to 400,000 people regularly go out hunting in Britain once or twice a week throughout the season, from November to April. Adding in the occasional hunters, the number approaches a million."

The sabs contend that 70 percent of the British population thinks the so-called "blood sports" should be abolished. A recent poll by the respected Market and Opinion Research International firm showed that nearly 60 percent of the respondents thought blood sports were "morally wrong."

But Tracey says, "Our own research tells us that 95 percent of the population doesn't even know what field sports are. So how can so many oppose them?"

Sabs, farmers and hunters also disagree over how harmful foxes can be. Mike Shepherd, who owns five farms around Surrey, watches the Saturday hunt every week with undisguised delight. "I'd like to see 'em poison the fields altogether," he says. "People who want to protect the foxes make me sick. Foxes are a plague. I had 300 sheep last year, and only 50 survived."

Wilkes disagrees. "I'm a town boy, but I've always been interested in animals. If you're interested, you know about them. These foxes around here do not kill sheep."

The Ministry of Agriculture in Britain does not register the fox as a pest, but does concede that foxes will eat sheep and fowl that are not kept in secure areas.

Early on Saturday afternoon, Chamberlain, Wilkes and Williams met up with Shepherd as they tried to follow the hunt. He blocked their car with his own. A policeman trailing the sabs finally had to cool things down. Squad cars are now a regular sight at hunts, as angry confrontations between hunters and sabs have become the norm.

"Look, you go your way," the officer told the sabs, "and you go your way," he said to Shepherd."Don't prevent each other from doing what you came here to do."

With a few parting shouts from the opponents, the cars moved off. But the hunt was now too deep into the woods below the road to see. It was near the end of the afternoon, anyway, so the three sabs decided to call it a day. They climbed back into the foul-smelling Ford, and started out on the two-hour journey home, eating crumbly potato chips and talking over the day.

They'd caught sight of the hunt just once in about eight hours, and had then managed to call away just two dogs. That made it, actually, a good day, according to Williams. "Lots of action," he said, munching happily. "Oftentimes we never even see the hunt, and we hardly ever know if we've saved a fox. We just hope."