In this booming, friendly, space-crazy town filled with the esprit of NASA, Lawrence Mulloy has developed a reputation as a hard-working manager, a Cajun with a self-deprecating sense of humor and a willingness to explain science to reporters, an engineer still thrilled with the increasingly routine launch of successive space shuttles he helped put aloft.

But since the routine was shattered Jan. 28, the esprit here has hardened into weary, closemouthed defensiveness. And Mulloy, the NASA official who reportedly pushed to launch Challenger despite the reservations of those who built its solid rocket boosters, has moved from relative anonymity to the center of controversy.

Morton Thiokol engineers, according to a National Public Radio report Thursday, have said Mulloy, chief of the solid rocket booster project at Marshall Space Flight Center here, met their concerns about cold weather and critical O-ring seals with the comment: "My God, Thiokol, when do you want me to launch? Next April?"

Mulloy, who has spent his 20-year NASA career building the rocket engines that have propelled the American space program, has refused to confirm or deny he made the comment. But it has focused the investigation into the shuttle explosion on Mulloy and his colleagues here and on the prelaunch disagreements with Thiokol engineers.

Mulloy, his superiors and others at Marshall are expected to testify at public hearings of the presidential commission Tuesday and Wednesday in Washington. Late last week, Marshall issued a blanket statement declining comment until then.

With many others involved in the launch talking, however, a NASA official here conceded that Marshall is being "flattened" by negative publicity and that Mulloy looks "particularly bad at the moment."

Since his central role became public, Mulloy, 51, has been the man everyone wants to talk with. Reporters have dogged his secretary, his former wife, his sons, the unfortunate man who now lives in the house Mulloy vacated when he was divorced last fall.

He promises on his telephone-answering machine that he'll return calls. But he doesn't return those from reporters. He isn't talking at all, not even to say he has nothing to say.

His reluctance to pause for the cameras and notebooks and issue a public "no comment" has led optimistic reporters to camp in front of his garden apartment.

Arriving home one night last week, he said he just wanted a few moments with his sons before talking to a pair of waiting reporters, but he never reemerged. A neighbor said that later that same night, he climbed out a rear window of his apartment to avoid the media waiting for him.

Those who know Mulloy say such behavior is uncharacteristic, but it mirrors the reaction of this town in response to an influx of out-of-town reporters with hard, often accusatory questions.

Those who live here and know the NASA officials resent the implications of what is being said about their friends. "It sure seems like they're pointing the finger at just one person," said Rozanne Yates, who lived next door to Mulloy and remains friends with his former wife.

The wife of an engineer who works for Mulloy said her husband would have nothing to say because he didn't like what was being said in news reports, but she described Mulloy as "a great guy, a fantastic guy, and a great technical man."

A large man, with the air of a former football player, Mulloy was born in Shreveport, La., and considers himself a Cajun. He served three years in the Army after high school, leaving with the rank of lieutenant, and subsequently took an engineering degree from Louisiana State University and later a graduate degree in public administration.

Mulloy has a pilot's license and likes to golf and cook. With some others, he owns a house boat, and former neighbor Ed Yates said he likes to cruise it down the Tennessee River with friends, tie it up and barbecue or shuck oysters.

The Yates said Mulloy normally has a fine sense of humor, which he is not afraid to turn on himself. Last February, while he was still living on the steep cul de sac next to the Yates, there was a heavy ice storm that made the street impassable.

A car struck Mulloy's Cadillac, causing it to slide down the street.

"He saw it, and came dashing out of the house in his bathrobe to try to save his car," said Rozanne Yates. "Well, his feet went right out from under him, and there he was sliding down the street in his bathrobe, with nothing on underneath."

"He just loves telling that story," she said with a grin.