The vehicle will be similar to the Tigra roadster, which will be built starting in September 2004 by Heuliez.
Opel must decide whether the Astra convertible will be built at its plant in Antwerp, Belgium, or in Bochum, Germany.
It is also unclear which firm will supply the roof system.
Porsche subsidiary CTS in Hamburg, Germany, believes it has a good chance of winning the contract, according to information from supplier circles.
Due to high logistic costs for the current Astra convertible model, which is built by Bertone in Italy, Opel CEO Carl-Peter Forster decided to produce the successor in-house.
Together with the three-door Astra GTC, the convertible coupe is designed to give the Opel brand a sportier image.