Discovery's successful launch pad test firing shows it's "a very good bird," the shuttle's chief says, but NASA has two major hurdles to clear before its first post-Challenger manned space flight.

Both could be resolved in the next week, and if they are, shuttle managers are expected to set a firm launch date of late September or early October for the crew of five astronauts."I still think we still have a shot at late September," Robert Crippen, deputy director of shuttle operations, said after Wednesday's 22-second firing of Discovery's three main liquid fuel engines.

The remaining technical problems are the repair of a small gas leak in Discovery's steering engine system and the final prelaunch test of the redesigned solid fuel rocket booster that caused Challenger's destruction 21/2 years ago.

Wednesday's firing not only tested the engines, but other orbiter systems, countdown procedures and the launch team, which has added several new faces since Challenger and its crew of seven were lost in the Jan. 28, 1986, explosion.

"We proved it works," said Crippen, a 50-year-old Navy captain who commanded the first space shuttle flight in 1981 and has been on more shuttle flights than any other astronaut.

"It's a clear demonstration that Discovery is a very good bird," added Thomas E. Utsman, director of shuttle management.

The flawless firing was a spirit lifter for space workers here who have had to overcome one problem after another since Discovery was moved to the launch pad July 4.

Mechanical and other difficulties had delayed the engine firing five times, and, combined with the unresolved gas leak, pushed Discovery's launch date off from early to late September, with October a distinct possibility.

Crippen said that while it would take several days to thoroughly analyze test data, "you can't have a major milestone like that come out as clean as it did and not feel good about it."

He said the only question that turned up in a preliminary look at data was a possible leak of nitrogen gas in an area where fuel lines join the external fuel tank. He said he did not think it was a significant problem.

Engineers will begin concentrating on the steering system leak early next week when they climb into Discovery's cargo bay with a plan to cut a hole in the rear bulkhead to gain access to an engine compartment.

The leak is in a fitting on a vent line, and the plan is to clamp a clamshell-like device around it and fill it with a sealing compound. The repair is expected to take about a week.

The fifth and final full-scale test firing of the shuttle's redesigned solid fuel booster rocket is set for Aug. 18 at the Morton Thiokol plant near Brigham City.