The failure of a French Ariane rocket to budge from its launch pad here Wednesday night was an embarrassing public relations blow but is not likely to dampen U.S. companies' enthusiasm for the U.S. shuttle's chief rival to launch their satellites, according to U.S. satellite executives gathered here.

Officials of Arianespace Inc., the privately owned rocket company spun off by the European Space Agency, said today they were still investigating why a ground valve malfunctioned at the end of the countdown, causing computers to halt the mission automatically five seconds before ignition.

Charles Bigot, Ariane general director, also disclosed at a news conference that a helium tank inside the rocket's cryogenic third stage depressurized too quickly after the mission was scrubbed, forcing ground controllers to intervene and slow the process.

But Bigot said the inquiry should not take more than five days and there was no immediate sign of any damage to the rocket or to the U.S. and Brazilian satellites it was carrying. "We have technical assurances that everything is in safe condition," he said. "I think we'll be able to launch again by next Friday," March 28.

Some U.S. executives here were not satisfied with the company's explanation. One noted that some computers continued to operate as though the mission was proceeding more than three minutes after it had been scratched.

"They're telling what didn't work but I want to know why they didn't know it wasn't working," said Rod White, manager of launch operations for American Satellite Co. in Rockville, Md.

Although delays are not unusual, the aborted launch was a painful reminder of the frailty of rocket technology, some executives here said. Hoping to capitalize on the grounding of the U.S. space shuttle fleet in the wake of the Jan. 28 Challenger disaster, Arianespace had flown in executives from Ford Aerospace, American Satellite and other communications firms to show off their new launch pad and demonstrate the reliability of their unmanned rockets as launchers of commercial satellites.

Atop the 160-foot, three-stage Ariane 3 rocket were two payloads -- one a $90 million GSTAR II telecommunications satellite owned by GTE Spacenet in McLean, Va. -- that Ariane planned to place in orbit 22,300 miles above the Earth. The scheduled launch -- Ariane's second since Challenger -- also brought an unusually large worldwide press contingent flocking to this steamy outpost on the fringes of the Amazon jungle.

Company publicists boasted beforehand that one major television network was planning to cover the liftoff on its evening newscast.

But while the guests in the VIP section of the control room looked on puzzled, the countdown proceeded to zero and the rocket failed to move. Instead of shooting flames and a ground-shattering blast, it sat silently on its launch pad.

"When the whole world is watching, this is not the time to have something like this happen," said John Fedak, vice president of Ford Aerospace Satelite Services Corp. "It's a unfortunate glitch . . . . I'm sure it will have a reaction in the insurance industry."

In an accident last September, while French President Francois Mitterrand watched from mission control, a hydrogen leak caused an Ariane rocket to veer off course, forcing ground controllers to destroy it when it appeared it might hit populated areas of South America. An $80 million GTE satellite was lost, prompting a sharp escalation in insurance rates.

But with the U.S. shuttle fleet grounded for at least one year and its commercial customers having nowhere else to turn, Ariane president Frederick de'Allest said here this week that the firm would have "no problem" filling the eight new launch slots it has opened up to accommodate post-Challenger demand.

"People have been looking at Ariane not because they have such a reliable launch record," said GTE Spacenet president Jerry Waylan. "They're looking because the space shuttle is down for one year and there aren't any viable alternatives."

"You know they talk a lot about all the wining and dining [Ariane officials] do down here," said White, whose firm is considering switching from the shuttle to Ariane. "But let me tell you, they don't have to do any of that, because people are beating the paths to their door."