Worried that sensitive aerospace data were being transferred overseas, the State Department has suspended all work between Boeing and its Russian and Ukrainian partners in a pioneering venture that would fire rockets into space from a floating platform at sea.

A State Department official said the department was working with the Defense Department and was passing along the results to the Customs and Justice Departments, which are looking into whether Boeing's transfers broke any American laws. Neither Boeing nor the government would spell out the nature of the offense that prompted the suspension. It was unclear whether the trouble was more procedural than substantial.The Boeing-led venture is known as Sea Launch. It seeks to adapt Ukrainian and Russian rocket technologies to tap an emerging market for the lofting of hundreds of communication satellites into orbit.

Boeing characterizes the work as turning swords into plowshares. Its Ukrainian partner, the Yuzhnoye design bureau and Yuzhmash production plant, once made the Soviet Union's deadliest missile, the SS-18.

A recent investigation in Washington over whether American aero-space companies aided Chinese rocket makers has brought the Boeing venture and similar endeavors under close scrutiny.

The suspension took place on July 27 and forced up to 40 Russian and Ukrainian engineers to leave the venture's home base in Long Beach, Calif., Timothy L. Dolan, a Boeing spokesman, said on Monday. Dolan had no estimate of how long the suspension might last or whether it would delay the sea rocket's inaugural launching.

But a government official, who spoke on the condition of anonymity, said: "This is a big project. We would not suspend it unless there were serious concerns."

The suspension was imposed without public announcement and was first reported on Saturday in The Washington Post.