LONDON, OCT. 30 -- A handful of mud-caked drillers working deep beneath the English Channel tonight succeeded where the Spanish Armada, Napoleon, Hitler and a small army of European Community bureaucrats all have tried and failed -- they linked Britain to mainland Europe.

The historic breakthrough is largely symbolic: tonight's link is only a two-inch-wide borehole and it will take another month for the connection to be wide enough for people to pass through.

By January, however, the channel tunnel, or "chunnel" for short, should be wide and firm enough for British Prime Minister Margaret Thatcher and French President Francois Mitterrand to meet and shake hands, and by June 1993 trains are scheduled to run both ways through two 32-mile-long tubes. A third tube is to be used for servicing the tunnel.

But two inches were enough tonight for the French to celebrate -- and for the British to ponder with ambivalence and even dread the prospect of a permanent connection to a continent they have always regarded with suspicion.

"Whether you like it or not," warned the British Broadcasting Corp. tonight, "Britain will be joined to France for the first time in 8,000 years," referring to the period when the last ice age ended. Its evening news program featured a customer at the Royal Oak pub near the site of the tunnel complaining: "We're supposed to be an island. Why the hell aren't we staying an island?"

George Walden, a Conservative member of the House of Commons, said he has received letters from constituents citing tabloid newspaper articles warning that rabies-infested French foxes will crawl through the tunnel to infect their English brethren and destroy British hunting. "It's a sort of primitive, emotional reflex that foreigners will infect our pure land," said Walden.

Some of that reflex was on display in the House of Commons this afternoon as Thatcher made a spirited defense of her decision to defy the 11 other member states of the European Community last weekend in Rome by voting against a plan for economic and monetary union. The question of the tunnel never arose, but the subject ultimately was the same: Britain's role in Europe.

There was much talk from Thatcher's supporters about defending the British pound from proposals to create a single European currency and of maintaining British sovereignty. There were also accusations of "betrayal" -- that Italy had conspired with the leaders of France and Germany to gang up on Britain and speed the pace of unification.

The tone was belligerent, the message one of mockery and defiance. Thatcher had come home from the Rome conference accusing the other European leaders of living in "cloud cuckooland." She invoked Britain's role as a lone bastion of democracy during World War II -- "this Parliament kept sitting when the lights of Europe went out," she said -- and suggested to the Commons that the country might have to stand alone again.

Both major parties remain deeply divided over Britain's future in Europe, and so opposition Labor Party leader Neil Kinnock was careful not to attack Thatcher's stand in Rome. Instead, he criticized her tough-talking style.

"Doesn't she understand that with her method of conducting affairs she is losing both potential allies and necessary influence?" Kinnock asked the House of Commons. "Her tantrum tactics won't stop the process of change. . . . All they do is to strand Britain in some European second division without the influence that we need."

Thatcher has supported the $14 billion Eurotunnel project, but critics contend her backing has been grudging and half-hearted, similar to the support she has given to European unity. While France's Socialist government is planning to invest more than $30 billion in a 2,000-mile high-speed rail network over the next decade, Britain's Conservative leadership recently refused to help finance a $7.4 billion high-speed link from the port of Dover, at one end of the tunnel, to London.

As a result, planners estimate trains will be speeding to Calais from Paris at 180 mph, tearing through the tunnel at 90 mph, then pushing on to London at less than 60 mph. Critics warn the backup of cars, trucks and buses on the overcrowded Dover-to-London highway could turn the scenic Kent countryside into a giant parking lot.

Alastair Morton, the outspoken British co-chairman of Eurotunnel, has compared the projected congestion to "thrombosis in the transportation corridors of southeast England, in our arteries. It threatens the heart of Britain." But despite government pledges to spend millions to upgrade the existing Dover-to-London rail link, Morton has warned that Britain could fall further behind France and Germany in economic development because of its failure to capitalize on the project.

"I think the government was wise to stay out of the tunnel project itself -- that could have become a bottomless pit," said David Owen, a former foreign secretary who today supported Thatcher's position on Europe. "But it's outrageous that we're not subsidizing the fast link."

Not all of Britain's aversion to the project is based on anti-Europeanism. The government refused to invest money in the tunnel because it believed private investors should fund the project and deal with cost overruns, which have nearly doubled the initial price tag. It has been reluctant to finance massive rail expansion and road expansions in part because of fears of damaging the environment and alienating residents in a region that votes strongly Conservative.

Still, despite official disclaimers, the British approach has always seemed timid at best, and downright hostile at times. When Mitterrand journeyed to Canterbury in February 1986 to sign the treaty authorizing the project, his Rolls-Royce was hit by an egg while a crowd chanted "Froggy, Froggy, Froggy, Out, Out, Out!"

At one point British workers fell four months behind in drilling due to problems with the wet, permeable chalk. They remain two weeks behind, while the French are 17 weeks ahead of schedule.

Walden said hostility toward France and Germany among his older constituents is palpable. But among those under age 60, he perceives a different attitude: "There's a huge range of people who do not hate the continent, who have traveled there and who may even find its rather nicer there than here. These people won't fear the tunnel, they will welcome it."