JACKSON, MISS. -- Of all the mysteries surrounding the kidnaping of Annie Laurie Hearin, wife of the man reputed to be Mississippi's wealthiest, the biggest one is why.

Despite the offer of a $100,000 reward and the payment of nearly $1 million to satisfy vague ransom demands, there has been no word from her abductor or abductors 3 1/2 months later.

"We still haven't come up with a motive," special agent Stewart Murphy of the Federal Bureau of Investigation said.

Wednesday was Hearin's 73rd birthday. But as the sprawling hackberry trees in the front yard of the couple's ample but remarkably unpretentious house take on the colors of fall in this Deep South capital, her whereabouts and fate remain unknown.

"We all recognize that time ain't on our side," said Robert Hearin, 77, a businessman who has built a fortune reportedly in excess of $100 million through oil, gas, insurance and banking investments. "I'm still hopeful, but it's just the most bizarre thing I ever heard of."

Annie Laurie Hearin, a tiny, frail grandmother stooped by scoliosis and arthritis, disappeared from their five-bedroom, 1930s brick house on the afternoon of July 26. It happened in the hour and a half after her bridge club and maid left but before her husband drove home in his 10-year-old Cadillac.

Her similar car was in the driveway, where it remains, but no one was home. "She evidently sat down after her last guest left and kicked off her shoes," Mary Alice Bookhart, who for 35 years was the local newspaper society columnist, said. "That was the thing that always puzzled me: I didn't see Annie Laurie leaving the house with her shoes off."

Ailing, Hearin doted on her five grandchildren and still sparkled among friends, but between the church luncheons and grandchildren's visits, she spent most of her time quietly at home.

Surprised not to find her there that afternoon, her husband called the police and summoned his son-in-law to hunt for clues. That was when they found the note by the front door, one of only two communications since Hearin's disappearance.

Crudely typed on a 1920s-vintage typewriter, the letter apparently had been shoved under the door as Annie Hearin was taken away. It warned against calling the police and listed 12 former franchise-holders in a company in which Hearin was principal shareholder until this week, School Pictures of Mississippi Inc. The letter said Hearin should "put these people back in the shape they was in before they got mixed up with School Pictures."

The 12 people it turned out, were being sued in state court here by the student-photographs firm for unremitted student deposits.

"I didn't know any of these 12 people on the list, and I hadn't been involved in the operations of School Pictures for the last five years," said Robert Hearin, who has a reputation for plain-dealing and quiet philanthropy.

FBI technicians identified tiny splatters outside the door and on the brick stoop as Annie Laurie Hearin's blood. They said the height of the spatters indicated that she may have been hit on the head.

In a house swarming with FBI agents, Robert Hearin waited and waited for a ransom demand. Finally, 20 days later, a letter bearing his wife's handwriting and postmarked Atlanta arrived. It appealed to Robert Hearin to do whatever the kidnapers wanted. Investigators see the letter as evidence that Annie Laurie Hearin survived her abduction, but they do not know how long.

Among other factors, Annie Laurie Hearin had with her no more than a month's supply of a medication for her ileitis, a chronic inflammation of the small intestines that requires daily medication. The prescription had just been refilled and could not be found in the house. Without it, she would die.

After receiving her letter, Robert Hearin, although still unsure of what was required of him, paid the dozen men on the list nearly $1 million, the total School Pictures was seeking in its lawsuits. All but three eventually returned the money.

A week later, Robert Hearin went public in what police officials termed a difficult effort for an angular, laconic man so unassuming that he often attends drive-in church services to avoid attention and so private he often fishes alone at the lake on the couple's country property. In a news conference, he begged for his wife's return and offered a $100,000 reward. Still no response.

For a time, more than 40 FBI agents across the South were assigned to the case, poring through Robert Hearin's extensive business dealings for signs of a soured deal or a disgruntled employee. One of the men on the list was called to testify before a federal grand jury but no charges resulted.

A handful of FBI agents still is assigned to the case, but there has been no further communication from Annie Laurie Hearin or her abductors. "The motive could be something to do with School Pictures, but there's the consideration that it could be a diversion," agent Murphy said.

Psychics have swarmed in with leads that have gone nowhere, and would-be informers call the police and FBI with tips that have not panned out. In an effort to shake out new leads, the Hearin family cooperated in the filming of an episode of the television series "Unsolved Mysteries" scheduled for broadcast next Wednesday.

Still, there were no known witnesses, and the closest thing to a lead was the sighting nearby of a suspicious white van a week earlier.

The Hearins' history contains little but two quiet, suburban lives. Annie Laurie Hearin was active in the Junior League, the symphony association and various charities. She played bridge twice a month with the same seven women for 30 years. She talked to their son, a lawyer in New Orleans, every Sunday and their daughter here more frequently.

Their son, Robert Jr., found himself remembering little things as he thought back to that day in July. He remembered that "Mama" told him he would have to wait for that crate of Mississippi tomatoes she had promised to send him on the bus because her bridge club was coming.

Mary Weathersby, the maid, said the Hearins would have been sure to go out to dinner on Annie Laurie Hearin's birthday and recalled how he always sent her flowers.

"I don't know whether she's alive or dead, and I wake up thinking about it sometimes," Weathersby said. "I get headaches and I never used to. I just go on like maybe she's going to be home tonight."