Stiff upper lips for Eurotunnel backers as building delays mount. Though construction has begun on the massive tunnel linking Britain and France, some people remain only lukewarm to the idea of connecting the two nations.

Molly Butcher slumped into a seat at the Eurotunnel Information Centre in Folkstone and scowled at the project's masterplan. ``It's a great feather in Margaret Thatcher's cap. But that's all there is to it!'' she said. ``I've been going to France on boats since I was a child. Isn't that still good enough?''

If the residents of Kent are a little grumpy about the Channel tunnel, it's not just that the construction project disrupts their beloved footpaths along Shakespeare Cliff overlooking the coast of southeast England.

Britain's island mentality is under assault. Many Britons don't welcome the prospect of breaching the great trench between England and France with railroad tunnels expected to ferry about 50,000 passengers a day between the two countries by the year 2000.

Lack of British enthusiasm for a Channel tunnel has scuttled previous attempts, including the British government's abandonment of a project in 1974. To prevent such political interference again, the concession for the largest development project ever undertaken in Britain or France was given last year to Eurotunnel, a private British and French consortium.

If construction timetables are met and financiers don't lose their nerve, the 31-mile-long tunnel will open in 1993.

But nine months after the digging began, construction delays have rattled some of the project's backers. The construction company, Transmanche-Link (TML), is three months behind schedule on the British side and six months behind on the French side.

Eurotunnel, the Anglo-French company licensed to build and operate the tunnel, issued a formal warning in August, claiming it would invoke financial penalties against TML if construction schedules are not kept. Continental European and American bankers backing the project have been careful to show support for the Eurotunnel. French and American engineers have said delays at the beginning of large projects are common and that the construction timetable anticipates such problems.

One officer for a Swiss bank participating in a syndicated loan to Eurotunnel told the Monitor that recent press reports in Britain about problems with the project had been exaggerated.

When Eurotunnel raised initial capital for the project in London and Paris last year, its prospectus promised attractive timetables to travelers. Travel time by rail and Hovercraft between London and Paris will be halved to only three hours. The time will be cut another 30 minutes if British Rail can match France's high-speed rail service between Calais and Paris.

Transit time across the Channel for car travel, including waiting time and customs, takes about two hours by Hovercraft and three hours by ferry. The tunnel's rail system will use high-speed shuttles to carry passengers and autos for a travel time of 1 hour and 15 minutes. The car terminals at Folkstone and Coquelles, France, will link up with each country's highways.

Promoters say Britain will benefit from improved acccess to European markets and more jobs once the tunnel's shuttle service in fully operating. The depressed economy of northwestern France will also enjoy an increased flow of trade and tourists, bringing more jobs and investment to the region.

Like the towns of Folkstone and Ashford on the English side, France's sleepy port city of Calais is gaining temporary new jobs from the five-year construction program. Local residents are also encouraged by plans for extending a superhighway into the city and the beginnings of a property investment boom.

But residents of Calais, like their English neighbors across the Channel, also have doubts about the project. ``Since the 19th century, there have been 28 attempts between France and Britain to build the tunnel,'' said Fran,cois Borel of TML. Many residents won't be convinced until the first traveler emerges from Britain.

Now the project is in the hands of British, French, American, and Japanese engineers - and some 10,000 construction workers expected to be employed on both sides by 1990.

Boring three parallel tunnels - two rail tunnels and one smaller service tunnel in the center - is not technically difficult, say engineers, But it is the first time that expensive tunnel-boring machines (TBMs) are being used on a project of this scale.

The biggest challenges for the construction company have been managing the project and keeping the $20 million TBMs operating in an watery environment. On the British side, engineers claim the layer of white chalk-marl which lies beneath the seabed is a tunneler's dream.

The actual rate of digging has been much slower, however, due to cramped working conditions and managerial inexperience. About 1.25 miles have been dug from England as of early September where the TBMs are now progressing at a rate of a little more than 110 yards per week.

After several months' delay due to equipment problems on the French side, the watery grey chalk has slowed down the boring machines and only 250 yards have been dug since January.

``This far surpasses the difficulties of the Seikan Tunnel,'' said a frustrated engineer for the Robbins Co. of Kent, Washington, the American manufacturer for two TBMs in France.

The 33-mile-long Seikan Tunnel links the northern Japanese island of Hokaido with the main island of Honshu. It opened in March this year after 24 years of contruction and is now the world's longest undersea tunnel, with 14 miles underwater. The undersea portion of Eurotunnel will be 10 miles longer, but is scheduled to be finished in one-fifth the time.