LAMPOC JUNCTION, UTAH, AUG. 30 -- The space shuttle program roared back to life in the foothills of the Wasatch Mountains today as a redesigned booster rocket sent a two-minute blast of flame, smoke and dust blossoming into a golden-brown bouquet over the desert.

"This is a day for a couple of grins," Rear Adm. Richard H. Truly, NASA's chief of space flight, said of the apparently successful test of the booster.

He and others cautioned that the National Aeronautics and Space Administration cannot decide whether the test is a complete success until engineers have taken the hardware apart and analyzed it. They emphasized that "mountains of work" must be done on a tight schedule if the shuttle is to make its target flight date next June. Today's test was the first full-scale firing of the redesigned booster.

Engineers have worked intensely for more than a year on the redesign, following findings by a presidential commission that a leak in a poorly designed joint in a booster triggered an explosion that destroyed the shuttle Challenger 73 seconds after it was launched on Jan. 28, 1986. The crew of seven astronauts died in the accident.

"This is just step one," said J.R. Thompson, director of the Marshall Space Flight Center in Alabama, which manages the booster program. But he smiled when he said it.

The 3 p.m. (EST) event took on the tension and carnival atmosphere of a real launch. An estimated 9,000 spectators filled cars four or five abreast for miles along the road to this remote site, about a 90-minute drive northeast of Salt Lake City. It is here that contractor Morton Thiokol Inc. manufactures the giant booster rockets.

Sirens began to moan over the slopes as the test coordinator said, "T minus 60 seconds."

The countdown proceeded smoothly through points at which it had to be aborted three times Thursday after a water hose leak and related computer problems.

At zero, a white flame shot from the rocket nozzle, billowed into blackish-gray and blasted a path several hundred yards up a slope. The heat turned the desert sand glassy. The blast carried with it a golden cloud of desert dust that the slope channeled upward and heat built into a tower several thousand feet high against a clear blue sky.

The roar of the blast, taking seconds to reach the viewing area 9,000 feet away behind protective earthen mounds, drowned out raucous cheering.

Truly, a former astronaut, stood with his left arm raised in what appeared to be a stiff salute. He was looking at his stopwatch while watching the rocket fire on the slope beyond. One of the early indications of a successful test is that it fired for the entire 120 seconds it was supposed to.

Observers also were relieved that there was no second plume, which would have indicated a leak.

The 14-story test booster, known as "DM-8" (development motor No. 8), was loaded with 1.1 million pounds of propellant, locked in a horizontal position and nosed into 5,000 cubic yards of concrete and steel to block its forward thrust.

In the first 130 milliseconds after firing, a device in the nose of the booster shot flame the 126-foot length of the interior, igniting the exposed surfaces of the rubbery solid fuel. In slightly over one-half second the entire booster was at maximum pressure of 930 pounds per square inch. The flame temperature reached 5,800 degrees Fahrenheit.

Guyford Stevor, head of an independent panel of experts set up by the National Research Council to monitor the redesign, called the new joint design, which has been controversial, "a reasonable compromise." He added that "engineers' understanding of how the joint works is so much better now than it was before Challenger that it's unbelievable."

Engineers for NASA and Morton Thiokol said they were anxious to get a look inside the booster. Some of them took a quick tour of the outside immediately after the test but the lingering heat kept them at a distance.

It will be days before they can break down the inside components and begin a methodical analysis of how well the new joints and other altered parts performed under the intense heat and pressure.

It will be three weeks to a month before the analysis is complete, officials said. Solid-fuel rockets are especially difficult to test, and engineers say they can truly judge them only in an actual flight.

Today's test did not measure the forces that would be imparted to the booster by the other parts of the shuttle -- which would be attached to the rocket at launch. The test also did not measure the pull of gravity or the changes in temperature that would occur when the shuttle rises through the atmosphere, according to Carver Kennedy, Morton Thiokol's vice president for space programs.

A new, $20 million test stand is being built on a nearby slope and will measure the structural stresses during an actual launch. In today's test there were 500 information-gathering sensors attached to the booster. The new stand will have 1,200 sensors.

The booster tested today was 90 percent similar in design to the one that will be used to launch the next shuttle, Kennedy said. There will be slight changes made in the interior insulation before the next test.

The booster test was aborted three times on Thursday because of problems resulting from a failed coupling in a water hose in the ground system that cools the booster down after the test. After the coupling failed, engineers had difficulty resetting the computers for the countdown.

The booster team spent Saturday and part of today making dry runs of the countdown to make sure they had understood and fixed Thursday's problems.

Engineers said they do not yet understand why hose couplings failed at two different points Thursday, noting that the system had been tested several times.

Because many Morton Thiokol workers are Mormon, NASA consulted with church representatives to make sure there was no problem with a Sunday test, an official said.

He said Mormon bishops in the plant assured NASA that the test was acceptable because their religion teaches "If your ox is in the ditch on a Sunday, you've got to go ahead and get him out."