NASA engineers have uncovered two different fuel leaks affecting the nation's grounded shuttle fleet, but agency officials said they would be patched quickly and that shuttles soon would be flying again.

Meanwhile, the head of the investigative team assigned to determine what went wrong with the troubled Hubble Space Telescope promised a congressional committee yesterday that he and his colleagues would pinpoint the error and fix responsibility for the blunder that has crippled the orbiting observatory.

The Hubble investigation will be "very embarrassing to someone or some group," said Lew Allen, head of the review and director of the Jet Propulsion Laboratory in Pasadena, Calif.

Allen estimated that the investigation, including experiments on equipment used to test Hubble's blurry mirrors, would take at least six months.

The problems with Hubble and the grounding of the shuttle fleet have raised new concerns about the ability of the National Aeronautics and Space Administration to manage a large and varied space program, including a planned space station and ambitious missions to the moon and Mars.

NASA officials expressed confidence yesterday that eight of nine scheduled shuttle missions would be flown this year. William Lenoir, NASA's head of space flight, said the shuttle Atlantis probably would launch its secret military payload and that the shuttle Discovery would deploy the solar probe Ulysses before the window of opportunity closes in October.

Tests yesterday on Atlantis, which sat on the launch pad at Cape Canaveral with its troubled parts wrapped in plastic bags, revealed a fuel leak in the umbilical system connecting the winged shuttle orbiter with its silo-shaped fuel tank.

The leak is in a flange in a pipe that delivers supercold liquid hydrogen fuel from the external tank to the main engines.

NASA officials said the leaky flange on Atlantis may be repairable on the pad simply by tightening bolts. However, Atlantis might be rolled back to its hangar for more-extensive repairs.

Tests on Columbia this week also uncovered a fuel leak in its umbilical system, which had been dismantled and flown from Cape Canaveral to a Rockwell International Corp. laboratory in California. The leak is not in a flange but in one of two small seals in a shaft entering the pipe carrying liquid hydrogen from tank to orbiter.

In a sense, that leak has been repaired, since Columbia's entire umbilical system was replaced by one taken from the shuttle Endeavour, still under construction in California.

Columbia's flawed umbilical eventually will be dismantled and subjected to more tests.

A common problem with the shuttles' fuel system would have been much more difficult to deal with, shuttle director Robert Crippen said. NASA engineers believe that no gross flaw exists in the system but that age or a loose flange caused the problems.

NASA officials said tests used to certify reliability of the umbilical system are under review and probably will be more aggressive.