When warm weather brings out the bicycles, many owners find problems ranging from flat tires to terminal rust. After a winter's storage most bikes need at least a tuneup.

There are half a hundred bicycle shops listed in area phone books, if you're not up to doing it yourself. A shop offers mechanics who fix bikes for a living and have the right tools and replacement parts.

Rates for a tuneup range from $10 for a single-speed at the Bicycle Exchange in Fairfax to $25 for a 10-speed at Exchange and Cycles & Sports on Wisconsin Avenue. Mechanics will check and adjust the brakes; clean and lubricate the chain, gears and cables; adjust the derailleur; check the tires and wheels and tighten loose nuts.

Other services, sometimes at an extra charge, include trueing wheels; adjusting the front wheel cones, headset and handlebars; and checking pedals, crank and accessories. Some places, like the Alpha Bicycle Shop in Rockville, don't have a spring tuneup service but will give a free 35-point safety check and recommend adjustments and repairs.

Some shops advertise same-day service, but don't count on it; others will give only a ballpark price for a tuneup.

Choosing a good bike shop is like looking for a good auto mechanic. According to Neal Conway, manager of The Bike Shop on P Street, NW, off Dupont Circle, "It's really hard to tell about a shop just from the surroundings. Customers should talk to the staff and, hopefully, to the mechanics to find out how knowledgeable they are. Talk about your bike's problems and listen to the way he talks about a solution." Conway and other shop managers agree that the bike owner should discuss services and fees to know ahead of time exactly what he or she is paying for.

Almost all bicycle stores offer a year's free service and adjustments on machines they sell. It's wise to take your bike to a shop that sells the brand you own.

The Washington Area Bicyclists' Association recently surveyed and evaluated area bike shops; for a free copy, send a self-addressed stamped envelope to Suite A, 1520 16th Street NW, Washington 20036. BACKYARD TUNEUPS If you are reasonably mechanically inclined, you should be able to do tuneup work yourself, according to many shop owners. There are several good books on the care and feeding of bicycles. The WABA, Open University of Washington and many adult education programs offer bicycle-care courses. Here are some general guidelines suggested by various local shops:

Make sure you have the correct tools, Marc Gregoire of Big Wheel Bikes in downtown Washington suggests a set of Allen (hex) wrenches, vise grips or pliers, quality screwdrivers and an adjustable wrench. "Most bikes today use metric nuts and bolts, so it's a good idea to get metric wrenches," Conway of The Bike Shop added. All the shops recommended a light-weight lubricant such as WD-40 or LPS-1.

Once you've got your tools and an open place to work, clean the bike thoroughly. Wash the frame with mild soap and water, using care about the headset and axles unless you plan to repack them with grease.

Take inventory. Check the frame for cracks at the joints. Look for frayed or broken cables, missing nuts, broken spokes and other broken or bent parts.

If the tires are flat or low, pump them up first to see if they go soft while you're checking out the rest of the bike. Check the tires for sidewall cracks, imbedded glass or sharp stones, and look for cracks in the valve stems. cIf you suspect that the tube is leaking, remove the wheel and pry the tire off the rim, take out the tube, inflate it and hold it in a tub of water. Bubbles will pinpoint leaks.

Once you know what the bike needs in the way of parts, you may get by with only one trip to the shop.

The chain is the weakest link in a bicycle and needs the most frequent attention. "The chain should be cleaned at least once a year -- more often if the bike is used a lot," said Barry Rivkin, owner of Metropolis Bike & Scooter on Capitol Hill. "A lot of people will pour oil right over the dirt and grit. That isn't even a good temporary solution."

Chains on single- and three-speed bikes have a master link that may be opened to take the chain off. In most cases, a spring clip holds the link together and can be pried off with a screwdriver. Ten-speeds have continuous chains from which a rivet must be punched with a special tool (about $5).

Once the chain is off, soak it in a solvent until all the road grit is out and it bends smoothly and freely. Gasoline is okay, but Varsol mineral oil or a commercial degreaser is better and far less dangerous, according to Conway at The Bike Shop. Without exception, bike mechanics suggest the use of WD-40 or a similar product on chain, gear and derailleur. "3-in-1 oil or motor oil is far too heavy," Conway said. "It won't penetrate into the chain links and it picks up a lot of road grit."

Removal of the gear cluster or freewheel and the derailleur is usually unnecessary. Both can be cleaned and lubricated by spraying with WD-40. Pearl Gregory, manager of Cycles & Sports, suggests using a stiff brush to remove the shellac that builds up on transmission parts. Freewheel and derailleur should move easily.

With the chain in place (remember that on 10-speeds it is threaded through the derailleur) and the bike propped or clamped so that the rear wheel spins freely, run the chain through the gears. Generally the derailleur has two screws that limit its movement; they should be adjusted so the chain rides smoothly on the smallest and largest gears. The same goes for the simpler derailleur mechanism on the crank of 10- and 15-speed machines. Inspect the control cables and give them a shot of lubricant where they enter the protective housings.

The brakes are an important part of the mechanism but usually require less maintenance. The brakes on single- and most three-speed bikes are internal components of the rear axle. They seldom misbehave, and if they do it usually means a stay in the shop.

Some three-speeds and virtually all 5-, 10- and 15-speed bikes have external caliper brakes with pads for wear and clean off any grease buildup. Dan Duggan of the Bicycle Pro Shop in Georgetown says that caliper brake adjustments "are made at the pads, usually with barrel adjusters." He says that the pads should clear the rim by an 1/8" to no more than 1/4". When released, the brakes should pop open with little or no slack in the cable.

Lubricate the lever and caliper pivot points, and check that the spring snaps the arms fully open. With center-pull and better-quality side-pull calipers, both pads should grip the rim at the same time.

Both wheels should spin freely. With the bike propped upside down or clamped to a stand, set the wheels spinning, one at a time, and listen for grinding noises. The wheels should spin for a couple of minutes with little or no wobble; if they grate or wobble; it could mean the bearings need work -- another job for the shop.

Chech and adjust the front wheel cones so they hold the wheel firmly on the axle but without any noticeable drag. The cones -- the two caps over the bearings on the front axle -- are best adjusted with the wheel removed. With that done, set the wheel in the fork and gently tighten the two outside nuts or the quick-release mechanism, being careful not to jar the cones. Slight wobbles can sometimes be corrected by tightening and loosening spokes; this takes a special tool and skill and probaby should be left to a shop. BICYCLE SET AND SAFETY Before taking off or sending the kids out onto the road with that newly tuned bike, be sure it's set up correctly for the rider. While seated, the leg should be fully extended with the ball of the foot resting firmly on the pedal at the bottom ot its downstroke. Adjustment of the saddle should be checked periodically, especially if growing children are involved. The handlebars should be tight and straight in the headset and adjusted to a comfortable position. Easy and unobstructed access to the brake and gear levers is essential.

How often your bike needs maintenance depends on how often you use it: Daily commuters should lubricate the chain and give the bike a quick inspection once a week, according to Jim Witkin of the Bicycle Exchange. Weekend riders should check their bikes out once a month, and occasional cyclists should inspect their bikes every time.

Check the brake mechanism and adjustments, tire pressure, derailleur and chain condition. Also tighten any loose nuts and bolts. Most shops recommend that bikes used daily be brought in for an overhaul every two years or so. An overhaul -- stripping the bike completely and rebuilding it with attention to the headset and wheel bearings -- costs perhaps $60.

Bicycle registration in this area is at best confusing. The District has a mandatory program that's casually enforced. The bike can be taken to any police or fire station, where the serial number and description will be recorded. A registration number be stamped into the frame and a sticker put on. Proof of ownersip is required. The $1 registration is good for five years.

There's no safety inspection involved, however. The District requires all bikes to carry a warning device, either bell or horn. Full reflectorization is required and lights fore and aft for night riding. District bike regulations are detailed in traffic safety leaflet No. 9, available at most bike shops, the WABA or the Bureau of Motor Vehicles.

Montgomery and Prince George's Counties have voluntary registration programs that, like the District's, are aimed at recovering stolen bicycles rather than safety. In neither county do you have to bring the bike along -- just walk into any precinct office with the serial number, fill out a form, and go home again with a sticker to put on the frame. The program is free in Prince George's County and costs 50 cents for three years in Montgomery County.

In Virginia, Fairfax County has no registration program, leaving that up to the various communities. In Fairfax City, take your bike to police headquarters, where the serial and number and description will be recorded, and your personal identification number engraved into the frame. You can also get a safety inspection there if you want.

In Alexandria, take your bike to the police station with proof of ownership. The police will record the pertinent information and give you a sticker for the frame. The costs is 25 cents a year. Falls Church residents need only walk into the treasurer's office, hand over 50 cents and the serial number and get a metal tag for the bike plus lifetime registration. Arlington County has a voluntary program. Like the other jurisdictions, there is no safety check; for 50 cents the county will record the serial number and bike description.

With all that done, your bike is ready for another season of economical transportation, fun and exercise.