The end of Britain's island reserve?

FOR centuries the English Channel has played a dominant role in European history. The 22 miles of water that separate England from France have kept the British an island people, aloof from the Continent.

To some, the channel is romantic. Vera Lynn used to croon sentimentally during World War II about the white cliffs of Dover.

To others, it is a challenge. Begoggled swimmers, their bodies plastered with fat to keep the cold out, like to break each other's records swimming it.

To Hitler, it was a major frustration. He could stand on the cliffs of the France he had invaded and look across to the homeland of the disrespectful British he sought to conquer. But the channel thwarted him, and instead, in time, bore the British, the American, and other Allied soldiers who sailed across it to reclaim Europe from Nazism's grip.

Romantic channel, defensive moat, or just a big old ditch with tricky currents of gray seawater -- the English Channel has been called all of these things. But the effect of its presence has been to set Great Britain apart, even in these latter years when Britain has been looking increasingly to Europe for new trading relationships.

Now the island isolation of the British may be about to get a jolt. Once again, there is serious talk of the project that has been mooted since Napoleon's time, a project to bridge over, or tunnel under, the English Channel.

At present, the cross-channel traffic is either by air or by seagoing ferry or hovercraft. Millions of passengers and hundreds of thousands of trucks already move in and out of Britain each year by boat across the channel. But that involves the folderol of boarding and disembarking, and official inspection.

What we may see by the 1990s is a cross-channel link that will transform passage between Britain and the Continent, perhaps even permitting motorists to drive their own vehicles directly between England and France.

British Prime Minister Margaret Thatcher and French President Franois Mitterrand have given the go-ahead to planning for such a link.

It is to be financed by investors, not by the respective governments.

Various groups have submitted plans, which are now being analyzed by the two governments.

One plan involves roadways carried by bridge from each shore to man-made islands about five miles out in the channel. Then cars would drive down spiral ramps into a 13-mile tunnel connecting the two islands.

Another plan envisions two parallel tunnels underneath the channel. Cars would drive onto electric trains that would shuttle back and forth through these tunnels at high speed and with great frequency.

Another design is for a multi-decked bridge across the channel's entire width, encased in a kind of giant plastic tube through which motorists would drive.

Yet another plan is for a combined road and rail tunnel under the channel. Other proposals have been submitted, too. In earlier years, other cross-channel plans came to naught. This time around, the idea seems to be getting serious attention.

In their China-coast colony of Hong Kong, the British laid a magnificent tunnel across the harbor floor, linking Kowloon and the mainland with Hong Kong Island. Technically, it was much easier than the channel project, but it shows what can be done.

Though you can swoosh through the Hong Kong tunnel in your car with great efficiency, many still love to ride the smelly, noisy old Star ferries across the harbor, appreciating Hong Kong's ever-spectacular setting.

If the new channel link gets built, there will probably be some who will still want to cross by ship.

But when Englishmen and Frenchmen can drive to each other's countries in less than an hour, the consequences will be far reaching.