Griffin also said he expects a newly appointed ''tiger team'' to quickly find and fix the cause of the foam loss, and did not rule out the possibility that the shuttle could fly again before the end of the year.

Nevertheless, the international space station team formally requested that Discovery remain at the station an extra day in order to transfer additional gear and supplies, in anticipation that another shuttle flight would not be coming soon.

Discovery, carrying mission commander Eileen Collins and six other astronauts, arrived at the space station Thursday for an eight-day sojourn. The crew members spent Friday moving a nine-ton luggage capsule into the station, preparing for a spacewalk Saturday and inspecting the underside of the orbiter for damage.

Mission operations representative Phil Engelauf said at a Johnson Space Center news conference that Discovery pilot Jim Kelly and mission specialist Charlie Camarda used the shuttle's new, 50-foot sensor boom to look at five nicks in the orbiter's underside heat shielding and two protruding felt ''gap fillers'' in the seam between two shielding panels.

None of the nicks was considered serious. John Shannon, the flight operations and integration manager, said flight controllers expect to clear Discovery late Saturday or early Sunday for landing at Kennedy Space Center.

Shannon said engineers counted only 25 ''small dings'' in Discovery's heat shielding - a reduction from the 150 dings, including large scars, that shuttles have averaged over more than two decades in flight.

''Discovery is the cleanest bird we have ever seen,'' Griffin told reporters in a telephone news conference from his offices at NASA headquarters. ''Almost everything we did to the external fuel tank worked.''

The unalloyed success of Discovery's first few days in space contrasted markedly with the anxiety on Earth provoked by NASA's Wednesday announcement that it was grounding the shuttle fleet because the external tank had shed at least four unexpectedly large pieces of foam insulation during Discovery's launch Tuesday.