ALL YOU'RE buying is time, when you buy a safe, says Jon Payne, owner of Professional Lockmasters in Rockville and president of the Maryland Locksmiths Association. "If what you locked up is attractive enough, it's not safe from anyone. Given the right equipment and enough time, a burglar can break through any safe," admits Payne.

The 1965 Brinks robbery in Syracuse, N.Y., proved the point. The burglars blasted through three-feet of concrete with an antitank gun.

"However, this is no excuse not to buy a safe," continues Payne. "It's important to secure your valuables. The question is where do you stop? Home safes have a good track record as protection because [supposedly] the public has no knowledge of its existence in the first place."

Safes can be built into your home: sunk into your concrete basement floor, or recessed into your walls and hidden by a picture. Free standing ones can be drilled into the floor of a bedroom closet or left out in the open, camoulflaged as a table. And for folks with large size silver pieces or antiques, most safe companies will sell you a vault door. But it's up to the homeowner to have a building or masonry contractor build the vault, itself.

Many of Washington's embassy residences store their good home silver in walk-in vaults, according to one area locksmith.

Safe sales have increased in recent years. George McClean, manager of White Flint Safe and Lock, attributes this in part to "that Welch guy." Bernard Welch is the Washington area burglar who was sentenced to 30 years in prison earlier this month in Montgomery County for armed robbery and burglary charges. He is currently serving a 143 year District of Columbia prison term in connection with the murder of Dr. Michael Halberstam. The D.C. conviction is under appeal.

"With a guy like that on the loose, people were worried. He didn't bother with safes. He just took what was right there in the open... anything that was readily available. It would have been too much time and headache for him to bother with a safe. He just went in empty-handed, grabbed the victim's suitcase, filled it up with what he could find and left."

Officer Warren Carmichael of the Fairfax Police Department confirmed this. "Welch's method was to get in and out as unobtrusively as possible. As far as I'm aware of he did not break into any safes."

Locksmith Jon Payne noticed a big increase in safe sales during the massive soaring silver prices two years ago which have now subsided. "We couldn't hold on to anything with a combination on it," he recalls. "I could have sold a cigar box if it had had a lock on it."

Other locksmiths and safe companies believe business is good because consumers cannot find a bank safe deposit box. Selma Sadack, one of the safe deposit custodians at Riggs National Bank (Dupont Circle branch) says the larger boxes don't become available that often. "You'd have to wait about six months to a year before a box is given up. Of course, the newer branches have more boxes than we do." By large boxes Sadack means those starting at 5-by-10-by-22 inches. Roger Connor of American Security Bank agrees: "The larger size safe deposit boxes are hard to come by."

Home safes are also appealing for the consumer who doesn't have time for two trips to the bank: one to remove the item and another trip to return it.

Safes are listed with Underwriters' Laboratories in one of two categories: fireproof or burglar proof. Jon Payne says that 99 percent of the time you can't have both. "They're a contradiction in terms. To keep a burglar out you need metal. To make something fireproof you don't want something with a lot of metal since it conducts heat."

Tom Black, president of Safe Masters in Southeast Washington, says that people have shifted their emphasis to burglar-proof safes. "They used to worry about fire, now most customers feel it's more important to keep out the burglar."

Payne warns that consumers should be wary of what brand of safe they buy. Although his store carries both American- and European-made safes, Payne believes that the superior ones are made by the Europeans, though American ones are improving. He explains: "Americans make safes to fit the specifications required by Underwriters' Laboratories (UL). There's little incentive for competition. In Europe, safe manufacturers are more creative. This probably dates back to the days when royalty requested an unpickable lock for their jewels, etc. It was an honor to be the locksmith who received the royal commission."

Payne adds that European locksmiths build safes that are burglar proof on all six sides, whereas Americans only burglar proof the front -- where the combination is. Dale McCleary, associate managing engineer in the burglary protection and signalling department at UL, said this is only partially true. "Our first three categories of safes are only tested on the face, but we have not neglected the body. The body must meet certain physical construction requirements.

"The more sophisticated categories of safes, however, ARE tested on all six sides. They are torch, tool and/or explosive resistant for 30-60 minutes, depending on the model." What's on the Market

* Standing record safes: Standing record safes run anywhere from $90 to $12,000. Most come on wheels to making moving them easier. Safe Masters carries an upright 3-feet high by 2-feet wide and 2-feet deep for sizable valuables. Store president Black says he designed the safe himself. "I used a special re-locking mechanism as well as 1/2-inch thick steel in the door -- heavier than most safes. The usual burglar attack involves a crow bar that pries open or breaks through the steel door. My steel doors can't be popped apart," he claims.Price: $850.

Virginia Safe & Lock Service in Fairfax carries record safes measuring 28 1/4-by-19 1/2-by-22 1/2-inches for about $550. These have a high resale value, says service manager Rudy Jones. "We will take back the safe after a few years and resell it.

"Very often what happens is that a customer decides to leave his bank safe deposit box and buy a small safe. Two years later his valuables have accumulated and he returns for a larger one." Virginia Safe & Lock will also rent customers a safe, while the customer's own safe is being repaired.

American Safe & Lock in Silver Spring carries standard fireproof record safes ranging in size from 15-by-12 1/2-by-9 1/2 inches to 63-by-45-by-29 inches.Price range: $200-$4,000. Some safes go as high as $12,000, but these are torch and explosion proof, explains service manager Mike Hobbs.

Metropolitan Safe & Lock in Riverdale, Md., carries steel recordsafes in varying sizes starting at $266. The $266 safe measures 15-by-12 1/2-by-12 inches and are fireproof for one hour. Larger standing safes (20-by-20-by-20 inches) cost $860 and up.

Shaw-Walker Safes in Arlington carries filing cabinet safes, called "Fire-Files." They come in letter and legal size drawers and run about $1,400. Letter size front-to-back files measure 10 1/2-by-12 3/16-by-15 1/2 inches and the legal size files measure 10 1/2-by-15 1/2-by-15 1/2 inches. The files also come in in side-to-side filing models. Branch manager Bill Straub cautions however that they are not burglar proof.

* Wall, floor and walk-in safes: These are hard to price since so many variables are involved: what kind of wall or floor you're drilling into; how much steel you want to use (obviously, the more steel, the better protected from the burglar); and in walk-ins, how many reinforcing rods (again, more is better against burglars).

The larger safes are particularly good for antiques, art collections and large pieces of silver -- platters, bowls, etc. They are also more economical than having two smaller safes.

Area Safe & Lock in Alexandria carries wall safes that measure four inches deep. "We don't get many requests for these since they are so small," says president Jack Hardy. "They are designed for jewelry, not for the family silver, which is what more people want today." The wall safes cost about $172. Hardy says that most customers are buying floor safes that measure 1 1/2-by-1 1/2-by-1 1/2 feet and cost about $450. Hardy also sells a safe that comes with a cabinet above it. "It doesn't look like a safe and customers usually disguise the top with a doily or lamp. The cabinet safe measures 15-by-12-by-18 inches and costs $375.

Virginia Safe & Lock carries a 16-by-16-by-4 inches wall safe for $172.

Professional Lockmasters' owner Jon Payne says a waterproof solid steel safe built into a concrete floor might cost anywhere from $160 to $1,000, depending on size. "We would completely encase the container in concrete and make it flush with the floor, so it doesn't show. I recommend an in-the-floor safe for someone with little money, but some valuables. Floor safes are covered on three sides, making it hard for the burglar to get at."

Lockmasters will sell you a vault door for $1,500. Payne estimates a mason contractor might charge as much as $2,000 to install.

American Safe & Lock's vault doors start at $1,800.

Condominium dwellers, although they own their building or apartment, may be out of luck when it comes to the larger safes, observes Tom Black. "There's often no place for them to put one. They have no basements and the walls are usually too thin to install a wall or vault safe," he says. However, some architects, Black says, are beginning to incorporate safes in new structures they design. Safe Notes

* Virginia Safe & Lock has one antique safe for sale. Service manager Rudy Jones says it was made about 1890 and has very thick walls (six inches). The lock contains brass tumblers. The safe measures 42-by-30-by-28 inches and comes with casters. Cost: $595.

* At a New York City safe store recently, the company vice president held a safe exhibit for "art" safes. He pointed out that the safes of earlier days were decorative pieces, often covered in elaborate metal scroll work. So he gave 13 artists old safes to decorate. The result was the "art safe" exhibit, a range of safes costing between $2,750 to $8,000. Most were good enough for storing home valuables, but not as secure as today's models.

As one locksmith observed, the safe is the last defense. A secure home should also have good locks on the doors and windows, maybe an alarm system. Some homeowners even install an alarm system around the safe itself.