Four times delayed in the last two months, astronauts Joe Henry Engle and Richard H. Truly flew the space shuttle Columbia into orbit today, only to have a fuel cell failure that threatened to shorten their five-day mission by as much as three days.

Engle and Truly quickly began shutting down the cell, one of three, to prevent an explosion that might end the flight in catastrophe. Flight directors immediately ordered the astronauts to fly what they call a "minimum mission," meaning that Engle and Truly will fly the rest of the mission on a day-to-day basis using a minimum amount of electricity to run instruments and power machinery.

"It is still possible that we will fly a full five-day mission," Flight Director Neil Hutchinson said tonight at Houston's Johnson Space Center. "If we stay up tomorrow, we'll assess the conditions in the spacecraft and ask ourselves the same questions again the next day. Each day, the potential exists for tomorrow to be entry day or to press on."

If either of the two working fuel cells shows signs of weakening, Engle and Truly will almost surely be called home Saturday or Sunday. If the two good cells keep on working the way they were tonight, Engle and Truly will probably stay in orbit as scheduled until Tuesday when they return to earth and land at Edwards Air Force Base in California's Mojave Desert.

"There's no reason to believe there's anything wrong with our two remaining fuel cells that can stop us from performing a normal mission," Hutchinson said. "I know the crew would like to see this thing go all five days."

If Engle and Truly are called home early, Hutchinson said they will be told a day ahead so they can accomplish as much of their "high priority" tasks as possible before landing. They also need the time to get ready for landing since there are only three times each day that the spaceliner passes over Edwards Air Force Base during the daylight hours necessary for a safe landing.

While Hutchinson said Engle and Truly will miss some of their objectives under the minimum mission plan, he pointed out that they won't miss much. He said the two fuel cells still give Engle and Truly enough electricity to exercise the shuttle's mechanical arm and to run most of the experiments they have planned for an array of five instruments aimed at the earth through the open cargo bay doors.

The five instruments perform radar mapping of earth terrain, measure carbon monoxide pollutants in the earth's atmosphere and read ocean color differences to pinpoint the movements of schools of fish.

"If I have to put a number on it," Hutchinson said, "I'd say we could accomplish at least 70 percent of our mission objectives in this minimum mission profile."

At 10 p.m. today, one fuel cell was producing 7 1/2 kilowatts and the other 8 1/2 kilowatts of electricity. This is enough to do almost everything demanded of the shuttle except run all five instruments at the same time the mechanical arm is being exercised.

Almost as soon as they reached orbit this morning, Engle and Truly had trouble with the fuel cell they call No. 1 in the cockpit of the DC9-sized spaceliner.

The fuel cells work by mixing oxygen and hydrogen in such a precisely controlled way that they react chemically to generate electricity and produce drinking water. On their third orbit, Engle and Truly noticed that the drinking water being produced by No. 1 fuel cell was acid and that the temperatures inside the fuel cell were running high.

By the time Engle and Truly were making their sixth orbit, the misbehaving fuel cell was so erratic that the astronauts were told to turn it off and switch to a standby cell for power. Usually, only one of the shuttle's three fuel cells are used at a time. The others are for standby for an emergency like the one today.

Once a fuel cell is shut down, it cannot be turned back on. The process of turning it off bleeds away all the oxygen and hydrogen to ensure that they don't make accidental contact and cause an explosion.

The faulty fuel cell failed when one of the lines feeding hydrogen to it caused a buildup of water in the cell that spilled over onto a manifold that is electrically charged. The charge caused the water to break down again into hydrogen and oxygen, which was a hazard because the hydrogen could have been ignited by the charge.

The fuel cell failure took shuttle flight directors by surprise. The cells have been used in 25 manned American spacecraft since 1965 and had never failed in flight before.

"The good thing about this is that the shuttle is demonstrating that it can sustain a fuel cell failure and keep running," Hutchinson said.

The mission began auspiciously enough. Trailing a plume of orange flame 600 feet long, Engle and Truly rocketed away from Kennedy Space Center into the blue Florida skies at 10:10 a.m., only 10 minutes later than scheduled.

The spacecraft rolled over on its back and the astronauts were on their way into space upside down.

Just after 3 p.m. they sent down a television picture of the open doors to give the world a view of their cargo bay. It showed a big radar dish at one end which will be used to map the earth's terrain. It also showed the 50-foot-long robot arm that they plan to exercise Friday.