"NEW LOCKS I don't have too many of, but I do have a fresh batch of bagels," said the hardware salesman munching on one of his own.

Despite this drollery, there are a number of new and highly effective locks on the market. Some are manufactured here in the States. Several others are produced elsewhere and distributed by U.S. firms.

Among the locks imported from abroad there are several from Israel. Vaultlock has a new system, developed by Israelis, which installs inside of a door. There are six bolts attached to the geared locking mechanism. When a key is inserted and turned, it activates bolts that move out in four directions, much like spokes radiating from a wheel. (As a matter of fact, Vaultlock is marketed in Europe under the name "Spider Lock.") This means that the door is strengthened on all sides. It also means that even if the hinge pins are removed, the door itself will remain in place.

Vaultlock president Richard Hoffberger notes that this lock instead of a ridged key has a dimpled key, difficult to reproduce. The drawback to the system is that since it's placed within the door, the door must be about 1 1/2 inches deep to accomodate the lock. Doors with panels cannot be outfitted with Vaultlock. The system costs about $450 installed.

Mul-T-Lock, also developed in Israel, is now manufactured here. Like Vaultlock, it is a "multiple point system" that can be put into existing doors or prefabricated doors.

Corporation president Leon Reich says that Mul-T-Lock can be installed on paneled doors. Installers "box-in" the inside of the door with steel. The panels on the outside are not touched. Depending on the kind of cylinder used with Mul-T-Lock, the system and installation cost $200.

An effective cylinder now widely available is manufactured by Fichet in France. The cylinder uses an unusual four-sided key that looks in profile like a capital "I." (It also makes the average key ring nearly impossible to fit in your pocket.)

Inside the cylinder there are two side bars and 10 levers. The side bars prevent an improper key from turning. The levers are thins strips of metal that function like horses on a merry-go-round. When they are all pushed into the "up" position by the key, the key can then turn freely. If they are not all aligned, the key will not turn. Most locks on the market have only one side bar and five or six pins.

Catch 22: The Fichet cylinder is only as effective as the dead bolt into which it is screwed. It costs $65. The cylinder and lock can run near $100. Despite the cost, New York City locksmith Brian Odowd says that Fichet's locks are "among the most resistant to force of any on the market."

"The Fix-It-Yourself Manual" (Reader's Digest, 1977) divides common, exterior locks into three categories:

* Rim locks have cylinders extending through the door. The lock is held in place by screws, accessible from inside the lock case. A ring on the front of the cylinder is designed to prevent tampering from the outside.

* Mortise locks are mounted in a recess, chiseled into the door's edge. A threaded cylinder is screwed into this unit and secured by setscrews. The setscrews are sometimes concealed by a false plate covering the face of the lock.

* Locksets, also called key-in-the-knob locks, have doorknobs on both ends. The keyhole is on the outside knob. Inserting your key and turning the lock releases a spring catch and opens the door.

Police Officer Herbert A. Smith of the 4th District's Community Services Division says that before buying any locks the neighborhood and the building to be protected must be considered.

"If you have good neighbors and your door's exposed and well lighted, you can use fewer locks," Smith says. "Of course if there is a pane of glass near your lock, you need one with a double cylinder -- one that's keyed on both sides. Even if someone breaks the glass, they won't be able to release the lock unless they have a key."

Smith also notes that "the bolt or throw should be at least one inch long," because in many homes there is a space between the door frame and the door, to allow for settling. "You want the bolt to bridge this gap and rest securely in the door frame -- not just in the molding, but in the door frame," Smith says. And it's always a good idea to check the door jam and molding for weak or rotting wood. If the jam is flimsy, a burglar can push against it. The lock will hold, but the wood of the jam will crumble and the door will open.

The Division of Community Services also suggests avoiding spring catches and locks with wedge shaped bolts. "Slant bolts" may be jimmied by a credit card or screwdriver. The same holds true for spring catches. But dead bolts with square corners must be thrown into place by turning a knob or key. They can not be disengaged with a chisel or credit card.

Officer Smith's final suggestion is that before buying a lock the consumer weigh the different models available. "If it's good and heavy, chances are it's a better buy than the lighter, less well-made specials." Common dead-bolt locks, usually installed in addition to key-in-the-knob locks, start at about $20 in local hardware stores.

Despite weight and cost, no one in the hardware business gives ironclad guarantees about any lock. As Charles Goldberg of Union Hardware says, "If a burglar really wants to get in, he may just find a way to get in. The credit card business is awfully simple."

Nevertheless, Goldberg recommends one lock to thwart intruders: the mortise. It usually comes with both a lever and latch, and a dead bolt in the same unit. This means you get the added protection of a dead bolt, without installing an auxiliary lock. On the outside of the door all you see is a knob and the lock cylinder. The mortise lock includes a spring latch, which can be engaged or disengaged by pressing two small buttons set into the door. This offers what Goldberg termed "a minimum of security with minimum effort."

Although the mortise lock is more expensive to install, Goldberg maintains that the the security it offers is worth the added expense. "It's not a surface mounted lock," he says, "so by bashing against the door you're not going to knock off the lock. With anything surface mounted, it's only as good as the wood of the door it sits on. But with a good mortise lock you'd have to destroy the door to pull the lock out."

There are other locks and cylinders available.

Combination locks, with a variety of buttons to depress in sequence, have been on the market for many years. They still represent only a small percentage of overall locks sold.

Their lack of popularity can be attributed to three things. 1) Combination locks are impractical unless you have a well-lighted exterior door. All too often people with combination locks on gates or doors have to strike matches so to see the buttons. 2) They are unattractive. The mechanism on the exterior and the interior of the door is bulky, and obtrusive locks are not appropriate on formal entrances. 3) They are not as safe as a mortise lock. One locksmith noted that if you drove a chisel between the door and the backing of the lock, you could probably pop it off.

But if you lose keys, or lock yourself out of your house a lot, combination locks can be an asset. If you're not good with numbers though . . .

There are numerous window locks on the market too. Roy Chappelle at Hechinger says the easiest to install and the most secure is called "Fayle-Safe." It comes with wooden screws that are inserted into holes, drilled through upper and lower window sashes. When the screws are in place, the window has in fact been bolted closed. The screws can only be removed with a special key. "Fayle-Safe" costs $3.29.

Sliding door locks come in a variety of shapes and sizes too. Eugene A. Sloan, author of "The Complete Book of Locks, Keys, Burglar and Smoke Alarms," says the most effective ones must serve two purposes: not only should the lock secure the door so that it can't be slid open, the lock should bolt the door down so that it can't be lifted off its tracks and simply removed.

Charlie bars, pieces of wood placed in the track of a sliding door to prevent it from opening, do wedge the door closed, but all a burglar needs is a screwdriver and a bit of brawn to yank the door off of its track. One patio lock that does prevent this is an L-shaped model that wedges and bolts the door in place. The "Deerfield Patio Lock" retails for under $20.

If locks are not enough to make you feel safe, there are alarm systems that work with magnetic fields or ultra-sound waves.

"Notifier" is available in wireless or wired models. It consists of a console with siren, and a transmitter which is placed on doors or windows. One part of the transmitter sits on the window, and lines up exactly with its mate which is attached to the window frame. If the magnetic field between the two is broken, the siren goes off. "Notifier" costs $119.95.

"Ultrason II," is even simpler to install. You plug it in and aim it at the doors or windows that need protection. It "blankets" whatever is in this field of vision with waves of ultra sound. If anything breaks through that field, a siren goes off. "Ultrason II" retails for $219.95. (One note of caution: My aunt and uncle have a system which works with ultra-sound waves. They also have several cats. The two are not compatible.) If you have mobile pets, a system which picks up any random movement probably is not for you.

One clever protective system, which only works on wooden doors, is battery operated and hangs on the door knob. If the door is forced or jiggled, an alarm goes off. "Door Alarm" retails for $21.95 and sounds like an ideal companion for travelers.