One was a copy of a 1954 Testarossa 250 model - an original can fetch about $11.5 million.

''They are extremely good copies right down to the chassis work, numbering and interior finish,'' a Modena policeman said.

''Often there is only a millimetre of difference in the size and parts.

''Only by looking closely at the metals used was it possible to feel the difference with a genuine Ferrari.'' The operation was run by two ex-Ferrari mechanics who had access to original designs.

They concentrated on prestige models of the 1950s and 1960s.

Two Swiss citizens are wanted for questioning about their alleged role in selling the cars.

Ferrari alerted the police to its suspicions of a sophisticated counterfeit operation after it received repeated requests for parts to rebuild a car, which happened to have an unexplained number of accidents.

Modena police said the business began legitimately, rebuilding damaged Ferraris.

But when the price for ''classic'' Ferraris rose rapidly, the car-builders decided to cater to this market.

Fakes were sold to collectors in Japan, Switzerland, Britain and the US.

Police were tracing how many copies had been put on the market: ''It could be about 40, but we don't know - each one is worth several hundred million lire.'' Ferrari said yesterday it was awaiting developments to see if it should take legal action to prevent its cars being copied.

Robert Brooks, head of the international auction house of the same name, said: ''The replica lark has been going on for some years. But usually . . . they are known to be replicas and priced accordingly.''