British Rail announced that a high-speed railway linking London to a tunnel beneath the English Channel will run partly underground because of concerns of environmentalists and residents.

"Two-thirds of the route will be in tunnels or cuttings, which stop noise, and 30 percent of the cost will be (spent) on environmental protection in one way or another," British Rail spokesman Malcolm Parsons said.Environmentalists objected to routes proposed by British Rail, arguing they would spoil the rolling green countryside in the county of Kent, and residents said property prices would sink when the trains began to zoom past their doorsteps.

The new plan, in which three tunnels totaling 25 miles will be built on the 68-mile route from the coast to London, will add $855 million to the estiamted $2.05 billion cost of the railway due to open in 1993.

Parsons said the trains, which can travel at speeds of up to 180 mph, will go no faster than 140 mph, and when they run onto a section of existing track near London's Waterloo station they will slow to 60 mph. The average speed will be 100 mph.

British Rail said the travel time from London to the channel tunnel, or chunnel, at Shakespeare Cliff near Dover, 77 miles southeast of London, will take 40 minutes. It will take another 20 minute to reach Calais, where the line reaches France.

The same trip now takes nearly two hours by train to Dover, plus an hour on a cross-channel ferry.

The new route runs through southeast London to Swanley, Kent, in a 17-mile tunnel. The link then parallels a highway, dipping into a 5-mile tunnel near Chatham. The tracks run overland to Ashford, Kent, where a 3-mile tunnel will be built.

The last 15 miles to the chunnel entrance will be above ground.