NASA officials, pronouncing last month's full-scale test-firing of a redesigned space shuttle booster "completely successful," expressed increased optimism this week that they will be able to resume shuttle launches as scheduled in June 1988.

"If we had to write a scenario for the results of this test, I would not have changed anything in the way it turned out," John Thomas, head of NASA's rocket redesign team at Marshall Space Flight Center in Huntsville, Ala., said yesterday.

Engineers from the National Aeronautics and Space Administration and contractor Morton-Thiokol have spent the weeks since the Aug. 30 test-firing in Utah taking the rocket motor apart and inspecting and measuring the effects of the fiery two-minute blast on the joints and other parts of the 126-foot booster.

This was the first full-scale test-firing of the new design. A flawed booster-joint design allowed the escape of hot gases that triggered the destruction of the shuttle Challenger on Jan. 28, 1986, killing the crew of seven.

All the critical rocket joints held their seals perfectly on Aug. 30, allowing gas no closer than three inches from the primary rubbery O-ring seals like one that failed on the Challenger flight, Thomas said.

Richard H. Truly, NASA's chief of space flight, told a House science and space subcommittee this week that testing and manufacture of the new boosters is the main schedule factor in the return to flight.

"The schedule is tight but doable, and we are moving ahead well," Truly said.

NASA still faces hurdles before the next flight, including at least three more full-scale test-firings of the booster, in November, February and March. Two additional tests are planned for April and May but are not considered mandatory before the next flight, officials said.

An independent panel of experts has urged that the agency do at least all five tests before the next flight.

The budget for the redesign is $460 million, including about $15 million for the Aug. 30 test.

Other factors that could affect the flight schedule are problems with the shuttle's main engines and other shuttle hardware, and a mountain of paperwork connected with a continuing review of shuttle components, according to Truly and others.

The new booster design includes a third rubbery O-ring seal around the booster joints, a bonded, self-sealing insulation, a metal "capture feature" to strengthen critical joints, and heaters to prevent the ill-effects of cold weather that affected the Challenger flight.

What the engineers have done, according to one independent expert, is to design the adhesive and insulation so that the new booster would work "if you didn't have the O-rings at all."

Although the Aug. 30 test was the first and therefore the most psychologically critical, he said, each future test has more stringent requirements. For at least two of them, the design, materials and parts must be obtained under the same quality control conditions as the actual flight hardware. "Everything will have to have a pedigree, with traceable paperwork," the expert added.

Engineers plan to induce flaws in future tests in order to study the design's performance under probable, worst-case conditions, which could produce a test failure and a schedule delay.

"This flaw testing gets into very lively discussion in the technical community. It's unprecedented in the industry," said one engineer working on the redesign. "All the old-timers blanch. But we think we're breaking good, healthy new ground," he said.