NASA managers are "leaning toward" an on-the-launch-pad fix for a fuel leak aboard the shuttle Discovery that otherwise could force a major delay for the first post-Challenger flight, sources said Saturday.

Three options are under study to fix the leak in a steering rocket system, and sources said space agency managers hope to make a decision on how to proceed by Tuesday. If an on-the-pad fix can be implemented, Discovery could be ready for launch as early as the third week of September, just two weeks or so behind schedule."We're leaning toward an on-the-pad fix," said one official who asked not to be named.

But no final decisions have been made and Discovery remains in danger of a roll back to the hangar for repairs, which would delay blastoff one to two months.

Engineers Saturday also reported work was on track for a ground-shaking test firing of Discovery's three hydrogen-fueled main engines July 30.

The test, called a flight readiness firing, or FRF, had been scheduled for July 28 but unfinished work in Discovery's engine compartment forced a two-day delay. Officials were concerned Friday that an additional delay might be imposed, but technicians were able to make up time overnight.

To practice procedures for the flight readiness firing, NASA engineers will conduct a full-scale dress-rehearsal countdown starting at 11:30 p.m. Sunday that calls for filling Discovery's giant external fuel tank Tuesday night.

The so-called "wet countdown test" will end at 7 a.m. Wednesday at the T-minus 10-second mark and if all goes well, a new countdown will start leading to the engine test firing three days later at 7:30 a.m.

The fuel leak is located in a half-inch fuel line fitting inside one of Discovery's two steering rocket pods, mounted on either side of the ship's tail fin, and it does not involve the shuttle's main engine system.

The pods are crowded with fuel lines, valves and tanks for 15 rocket engines and the leak is located in an area that cannot be easily reached without first taking the pod off Discovery. And that cannot be done at the launch pad.