The Fairfax County Police Department almost had given up on solving the April, 1981, murder of the clerk at the Telegraph Road 7-Eleven convenience store. They had no suspects, no witnesses and no leads.

There was only one hope left: ask the public for help.

So police advertised the case in local newspapers and over television, offering a $1,000 reward for information on the murder. Within days the telephone call came: Two men had been boasting to friends for months about having pulled off the murder, and one of the friends decided to turn them in.

Why? "For the money -- no other reason," said Capt. Michael Young of the Fairfax police criminal investigations bureau.

It is all part of a program popularly called Crime Solvers, in which police offer cold cash supplied by local businesses for hot tips on cases where leads have run dry. The tipster is guaranteed anonymity, is given a number for identification and collects the reward if his information leads to an arrest and indictment.

Over the past four years, Crime Solvers has become an increasingly important tool for Washington area police. Almost $100,000 has been paid anonymous tipsters through Crime Solvers programs run by police in Alexandria, the District and Fairfax, Montgomery and Prince George's counties, police records show.

In Fairfax, Crime Solvers has paid $29,700 over the past three years for information that police say has helped in closing 303 cases and recovering $301,153 in stolen property. The fledgling 11-month-old Alexandria program -- the newest in the area -- has paid $3,900 to anonymous callers who helped police close 70 cases and recover $40,000 in stolen property.

Only a small percentage of the callers actually receive rewards, police records show. Fairfax Crime Solvers has paid 85 tipsters in the past three years -- about 5 percent of the 1,623 calls logged. In Alexandria, 11 of this year's 123 callers received rewards.

The money is donated by businesses and civic groups. Police provide only the manpower to handle the Crime Solvers telephones and to research the crimes. A civilian board, composed primarily of local business leaders, decides how much each caller will be paid and makes the payoff.

In a typical payoff, a board member might wait for the informant to approach him at the manager's booth of a local grocery store. The informant asks for the board member by name, and the board member asks the tipster for his assigned number. The informant then signs his number to a receipt and leaves the store with the reward.

Police concede that much of the reward money goes to criminals and friends of criminals. Callers frequently are partners in crime who believe they were cheated of their fair share of the take, police say.

"Usually the callers who give us the best information are at least on the fringe of the criminal element," Young said. "The person has to have access to be able to give us that type of information."

Fairfax Crime Solvers coordinator Richard D. Crosby described his typical anonymous caller: "They want their bucks. They're speaking in hushed tones. They may even be in the same house of the person they're turning in."

Girlfriends snitch on boyfriends, neighbors turn in neighbors, wives report husbands. A woman in Fairfax, angry that her husband hadn't come home in four days, called Crime Solvers to report he was making PCP. She sent police to the location, where her husband was arrested and the PCP confiscated. The wife later collected the reward.

Or take the case Montgomery County Crime Solvers coordinator George C. Heinrich faced two years ago. The state of Alaska had shipped a team of prize-winning huskies to Washington for President Reagan's inaugural parade, only to have three of the curly-tailed dogs stolen the day before the parade from a Damascus farm where they were being held. Police had no leads, and members of Congress were demanding fast action.

Police took the case to the television station that aired a "Crime of the Week" series and offered a $500 reward for information on the whereabouts of the huskies, valued at $5,000 each.

A few hours later, a woman called police to report she'd discovered the dogs in her basement. She turned in her two sons, who were charged with larceny. She collected the reward, and the huskies made it to the parade on time.

A large percentage of callers phone in tips just to help police, Crime Solvers coordinators say. "Occasionally the little old lady next door sees a drug buy go down in front of her trailer," Crosby said.

Edward J. Johannemann, coordinator of the Alexandria Crime Solvers, estimated 20 percent of the callers aren't interested in collecting reward money. "They're just the type who know and hear things but don't want to have to get involved in court," he said.

But police overwhelmingly attribute the success of the programs to the cash rewards. Payments usually range from $100 to $1,000, depending on the value of the information supplied and the seriousness of the crime. Fairfax Crime Solvers, for example, paid $5,000 to an informant who led them to the murderer in a Centreville case earlier this year.

John Love, supervisor for security for a grocery store chain in Maryland, has been making payoffs for the Prince George's Crime Solvers for almost five years. Love said his conversations with the tipsters at the pickups are usually terse.

"I say, 'Have a nice day and call again,' " he said. "Many of them never even say thank you; they get the money and take off."

But there is the occasional friendly informant, he said. He recalled an elderly woman who picked up her $300 reward and then convinced Love to buy a box of the cookies she was selling for a church fund-raiser.

Many informants are suspicious police will be lurking around the store trying to learn their identity, Love said. "One guy rented out a car because he was so suspicious that we'd check his license plates and find out his name," he said.

But the success of Crime Solvers, pioneered in Albuquerque in 1976 and now used by 320 police departments throughout the nation, is based on the anonymity afforded callers, police say. If a tipster gives his name, it's ignored. Instead, he's assigned a number.

"We don't want the courts to be able to subpoena anything out of our files," Crosby said.

Crime Solvers coordinators say the first year is usually the toughest for the programs. It usually takes a few years before the programs can build a large financial cushion as insurance for those occasional weeks when several major crimes will be solved simultaneously.

Alexandria Crime Solvers, as the newest in the area, has a large enough reserve to meet reward payments but is conducting aggressive fund-raising efforts, Johannemann said. "We'd like to have a cushion of $5,000 to 10,000," he said.

Donna Aldridge, an attorney who sits on the Prince George's Crime Solvers civilian board, said that county's group is turning increasingly from businesses to private citizens for donations.

"We have a core of businesses that seem committed because of civic interests," she said. "But we want to broaden the support in the community."

A mainstay of the Crime Solvers program is the "Crime of the Week," usually a particularly serious crime that has stymied police investigators. Crime Solvers advertise the crime on television and in local newspapers. Information leading to the indictment of a suspect in the crime of the week nets an automatic $1,000 reward.