Europe this week will launch its biggest, most versatile rocket ever, which could give it an edge over the United States and other countries in the race to commercialize space.

Ariane-4, which is to blast off Wednesday from the European Space Agency's space center in Kourou, French Guiana, was declared ready for service on Saturday. Fueling of the rocket began Sunday.The new generation rocket is designed to serve as Europe's "workhorse on the world launch services market until the end of this century," according to officials at Arianespace, the commercial arm of the 13-nation European Space Agency consortium.

The rocket will on its inaugural launch carry an international payload of three satellites into orbit, demonstrating the vehicle's space readiness to potential customers.

Capable of carrying heavier payloads than previous Arianes, the rocket is the most sophisticated the Europeans have ever produced. Its design allows engineers to strap on different configurations of solid and liquid boosters, tailoring the vehicle to a client's specific budget and needs, the agency said.

Developed over the past six years at a cost of $575 million, Ariane-4 can carry a maximum load of 4.6 tons into orbit. Ariane-3, the previous generation, had a maximum capacity of 2.8 tons.

Arianespace already hauls half the world's commercial payloads. As of May 25, the company held 67 launch contracts worth $3.4 billion.

The United States and Japan have barely entered the race. But in the coming years, Arianespace faces competition from the American Titan-4 made by Martin Marietta Corp., Atlas-Centaur built by General Dynamics and Delta made by McDonnell Douglas - as well as from the Soviet Proton, the Chinese Long March and the Japanese H-2, now under development.

The United States had been depending on its space shuttles as the chief launchers of commercial satellites until Jan. 28, 1986, when the shuttle Challenger exploded.