French and British workers on Wednesday finished drilling the first main rail tunnel that will provide high-speed train service under the English Channel.

The breakthrough came at 11:30 a.m. (2:30 a.m. MDT) when the massive digging machine Europa chewed through the last few feet of blue marl about 50 yards under the seabed, said the project's owner, Eurotunnel.The channel tunnel - called a chunnel by many - is the world's largest engineering project.

When completed in 1993, it will permit high-speed trains to travel between London and Paris in 31/2 hours - half the time it now takes to travel between the cities by train and ferry.

The most dramatic linkup came last fall, when workmen connected the small maintenance tunnel serving the two main rail tunnels. It gave Britain its first land bridge with mainland Europe since the last Ice Age, 8,000 years ago.

The breakthrough Wednesday came in the northbound tunnel. The southbound passage is expected to be completed by June 20.

Drilling is three months ahead of schedule, and many of the 5,000 workers will soon be laid off.

Track and signaling equipment then will be installed for the trains that will run from Sangatte to Folkestone, England, 31 miles away.

Huge terminals where motorists and truckers will load their vehicles aboard special rail cars are being built in both cities.

Nine workers have been killed during the chunnel project. The cost has climbed from an initial estimate of $8.2 billion to $12.8 billion, and fares still have not been set for the tunnel.

The French see the tunnel as a way to bring visitors in to revive depressed northern areas.

But the British are worried that the new route to their island will bring drug traffickers, terrorists or rabid animals.