A recent string of multibillion-dollar U.S. space launch failures can be traced to flawed workmanship and engineering by the contractors who built the Titan IV and Delta III rockets, a Pentagon study concludes.

The report released yesterday also cites the government's fragmented lines of authority for overseeing the space launch program.

"There is an urgent need to clearly identify authority and responsibility" for putting satellites into proper orbit, the report says. It also says the Air Force has allowed its in-plant engineering support to erode.

The Air Force ordered the study after a Delta III rocket malfunctioned in May, leaving a commercial communications satellite in a useless, lopsided orbit. It was the fifth failed space launch since August 1998 and the second botched flight in a row for the Delta III, built by Boeing Co.

The trouble dates to Aug. 12, 1998, when an Air Force Titan IV rocket carrying a spy satellite blew up less than a minute into its flight.

An Air Force investigation uncovered faulty wiring, as well as questionable quality control by Lockheed Martin Corp., the manufacturer. A Titan IV carrying a missile launch detection satellite failed on April 9, and a few weeks later another Titan IV put a military communications satellite in a wrong orbit.

In a letter to Defense Secretary William S. Cohen, President Clinton said he is pleased that the Air Force study has identified the root causes behind each of the recent launch failures and that corrective action is being taken.

"Now and in the next century, our national security, civil and commercial space sectors will continue to depend on reliable access to space to achieve our broader national goals," Clinton wrote in the letter, released by the White House yesterday.

Clinton said his science and technology adviser, Neal Lane, and his national security adviser, Samuel R. "Sandy" Berger, will review the Air Force report.

The report concludes that the main causes of the rocket failures were related to engineering and workmanship flaws at the factory. The shortcomings seem to have arisen from a premature shifting of attention--by both the contractors and their government overseers--away from executing successful launches with existing rockets to the future task of using a new generation of launch vehicles, the study says.

It cites a "premature 'going-out-of-business' mind-set," particularly in the Titan IV program. That program is "chronically understaffed," it says.

The report also raises concern about the risk of failure in flying the fleet of 39 existing Titan, Delta and Atlas rockets, which are valued at $20 billion and include critical systems with no spares.