It ripped across Northern Virginia like a chilling winter storm: The burglary scare, the race to install burglar alarms, the run on bank safe-deposit boxes, the neighborhood crime-watch frenzy, the rash of anticrime ordinances.

Burglary had gone beyond the dry crime-report statistics. It was hitting home for thousands of Northern Virginians.

"Until two years ago, we could predict which neighborhoods would have the most trouble: the affluent ones," said Greg Kurasz of the Arlington Police Crime Resistance Unit. "Then it became a shotgun effect. They were all over the place."

In the five years from 1976 to 1980, the number of burglary reports rose dramatically throughout the area, according to data compiled by the Northern Virginia Planning District Commission. Reported burglaries of homes and businesses in Loudoun County were up 633 percent. Home burglaries in Fairfax County jumped 108 percent.

Then came the local burglary scam that breathed even more life into the statistics: the story of Bernard C. Welch, the master thief who drove a Mercedes and lived in an imposing house in an affluent Great Falls neighborhood.

Welch's immense burglary operation was exposed last December when he was charged with -- and later convicted of -- the murder of Dr. Michael Halberstam in the District. Police discovered more than $4 million in allegedly stolen goods stashed in the basement of Welch's home. Law enforcement officials traced some of the property to dozens of burglaries in the Washington area, most committed in the four months before Welch's arrest.

The Welch case was a catalyst that the crime statistics couldn't match. Homeowners, businessmen and lawmakers began fighting back.

"People were sick and tired of letting criminals have their way and having to live in fear," said Conrad Marshall, president of a Great Falls neighborhood watch group, formed shortly after the Welch expose.

Now the fight is beginning to pay off, according to area law enforcement officials.

For the first time in more than five years, the number of burglaries in most Northern Virginia jursidictions has begun to fall, according to a survey of local law enforcement agencies.

Burglaries reported in Fairfax County during October were down 45 percent from October of last year. Break-in reports dropped 20 percent in Alexandria and 11 percent in Loudoun County during the same month, compared with 1980.

Law enforcement officials attribute the decline to a wide range of factors.

New laws regulating precious-metals dealers were adopted by most Northern Virginia jurisdictions last winter, in an attempt to stem the flood of silver, coin and jewelry thefts from homes. The Virginia General Assembly also approved a similar measure and it became state law in the spring.

Dealers now are required to hold precious metal items 15 days before reselling them or melting them down, and they must register each item and background information on the seller with authorities.

"If a seller is moving around and his name keeps coming up on the computer, we get suspicious," said Carlton King, commander of Fairfax County's Reston substation. "Some good suspects have been developed and arrested through the use of the ordinance."

During the past few months, law enforcement officials in several counties have nabbed several professional burglars -- burglars and burglary rings they say are responsible for dozens of crimes each. One of the most publicized cases involved Billy the Kid, a professional burglar arrested last summer and blamed for more than 200 burglaries in Northern Virginia.

"You take some of these people off the streets, and you often see a decline in burglaries," said King.

Fairfax County police attribute some of the drop in reported burglaries to a special squad of 20 off-duty patrolmen who were paid by the county Board of Supervisors to cruise high-risk neighborhoods during the afternoon and evening from June through September. Fairfax police records show the greatest decline in burglaries occurred from July through October.

Police also cite psychological factors to explain the recent decrease in burglary rates.

"Now there is more of an awareness that people's chances of being burglarized are a lot greater than they ever thought before," said Larry Garner, crime prevention coordinator for the Fairfax County police. "People are fed up with the idea that someone can go into their house, take everything they've worked a lifetime for and walk out with it."

Neighborhood crime-watch committees have sprung up across Northern Virginia. In Fairfax County, where the first group was organized two years ago, the number of community patrol organizations has almost doubled in the past six months alone -- from 93 last spring to 149 organized groups at present.

"I'm inclined to say the neighborhood watches are definitely helping," said King, although he added that the police department has no statistics to support that supposition.

Neighborhood watches are just starting in Loudoun, where police officials are training 30 "block captains" to lead the groups. Six watch groups are operating in Arlington, with five more gearing up, law enforcement officials said. One community-watch organization has been operating in Alexandria for almost two years, according to police there.

Some homeowners haven't waited for groups to be organized in their neighborhoods. Local installers of security systems say business is booming.

Although neighborhood groups may deter some potential burglars, police say once a home is burglarized there is little chance of recovering the stolen items. Fewer than 6 percent of all jewelry, precious metal articles, television sets or firearms stolen in Northern Virginia in 1980 were returned to their owners, according to reports compiled by the Planning District Commission.

"Everybody wants some kind of security system," said James Robinson, who operates a security system outlet in Falls Church. "They don't know too much about the different systems, but they know they want something."

Robinson said his business has doubled in the past two years.

A spokesman for another agency that installs security systems throughout the area noted, "There's been a big increase in our business ever since that doctor (Halberstam) got killed over in Washington."

Area bankers say they have backlogs of requests for safe-deposit boxes.

"We have waiting lists ranging from three months to two years, depending on the size box you want," said a spokeswoman for the National Bank of Fairfax. "There's always a waiting list."

Bank officials say although the demand for safe-deposit boxes has exceeded the supply for several years, requests have ballooned in the past year.

Other factors contributing to the burglary rate are out of the control of either police or homeowners, law enforcement officials admit.

The volcanic rise of gold and silver prices sparked a massive upsurge in silver and gold thefts a year ago.

"But if you watch carefully when the silver prices are down," said King, "you may see the next trend is in the theft of appliances, cash or firearms -- there's always a good market for firearms."

And the work of other law enforcement agencies can mean problems for the suburban districts, King said.

"If the police in the District crack down on heroin, the price is going to go up," said King. That often translates into more robberies in Fairfax to pay for the higher-priced heroin, he added.

Despite the steady drop in reported burglaries, law enforcement officials are reluctant to express optimism. They say the trend could reverse as quickly as it began.

Last spring, two months before the decline in Fairfax County burglaries began, the county experienced one of its most dramatic increases in burglaries in years when April reports esclated 43 percent over those in April 1980.