Although old bathroom or kitchen faucets that leak, drip or make strange noises when in use usually can be repaired, sometimes replacement parts are hard to find, and disassembling the old faucet is difficult. Very often the easiest solution is to replace the entire faucet with a new washerless model that will minimize maintenance problems and look a lot better than the old one.

New bathroom and kitchen faucets cost from $20 to as much as $60 or $70, depending on style and brand; the most widely sold models cost $30 to $50. Until recently, most faucets were available only through plumbing-supply houses that sold to the professional plumber, because replacing a faucet was not considered a do-it-yourself project.

However, since the cost of having one installed often costs almost as much as the actual faucet, many homeowners now are tackling this job themselves -- partucularily since manufacturers of faucets have introduced special models that are easier than ever for an inexperienced home handyman to install. The new faucets, which eliminate the need for special tools or unusual skills, come with flexible water-supply pipes that can be connected quickly to most existing valves or pipes.

In most cases, all the adopters and connectors needed are supplied, but in the few cases where they are not adequate to make the required connections, the dealers who sell the faucets (hardware stores and home centers) also sell an assortment of easy-to-use plastic and metal adapters and fittings that will solve the problem.

Although there are dozens of brands of faucets that fit into the do-it-yourself category, the companies that have been particularily active in desigining and packaging their faucets specifically for home installers are the Peerless Faucet Co. (Div. of Masco Corp., Indianapolis, Ind.) and the Fillpro Division of JH Industries, Inc. (San Marcos, Calif.).

Peerless makes kitchen and bathroom faucets, washerless and with washers (brass or neoprene), as well as single-handle washerless models. The faucets come with flexible copper water lines that are easily bent to make them line up with the exisiting supply valves or pipes.

Special plastic quick connectors that can be tightened by hand to connect them without tools are supplied and there is even a plastic wrench to tighten the nut under the sink that secures the faucet to the sink top. All this makes it possible to fulfill the company's claim that a person can install this faucet without any tools -- after removing the old faucet (you will need tools for that part of the job.)

The Filpro company has just introduced a new bathroom faucet, the Enduro, which incorporates as unusual mounting method that eliminates the need for reaching up under the sink deck to tighten the nuts normally used to secure the faucet to the sink top. A metal tiebar and two bolts are inserted while you work from the top of the sink. The bar, with a bolt protrudding from each end is pressed down through one hole in the sink and then turned so the one bolt sticks up through the other hole while you hold onto the second bolt (to keep the tie-bar from falling).

A gasket is then placed on top of the sink deck to hold the bolts in plasce, while each is individually tightened from above. This draws the tie-bar up aginst the underside of the sink deck. The faucet base is then screwed down on top of the gasket, after which the faucet body can be fastened down.

The Enduro faucet comes with two lengths of flexible plastic tubing attaching to the body -- one for hot and one for cold water. These water lines not ony make it easy to connect them directly to the existing water-supply valves or pipes under the sink, they also eliminate the need for washers or other valve mechanisms to control the flow of the water. A special internal cam pinches each tube to shut off the flow of water and releases it to increase flow.

According to tests made by the manufacturer, the special tubing used will withstand pressures of up to 840 pounds per square inch (household pressure never exceeds 60 psi), and the mechanism should give it in about 100 years of normal use.

When shopping for a kitchen faucet, it is important to buy one that has its connections spaced the same distance apart as the old one so it will fit the holes in the existing sink -- unless you are planning to buy a new sink at the same time.

Very often getting the old faucet is the hardest part of the job because the threads on the connections or the locknuts that hold it in place are rusted in place, and the nuts or bolts that hold it in place against the sink deck are often awkward to reach.

Start by shutting off the water-supply lines, usually by closing the valves under the sink where the pipe comes out from the wall. If the sink does not have its own shut-off valves underneath, you will have to shut off the main water-supply valve to the entire house.

After the water has been shut off, disconnect each water line from under the faucet. It is a good idea to place a pan or bucket where it will catch any water left in the pipes as you do this. When loosening the connections, two wrenches often will be required, one to hold the pipe and another to turn the fitting, one to hold each half of the fitting in some cases.

Loosening the locknuts under the faucet so the faucet body can be taken off is often the hardest part of the job. If you cannot reach up under the area where these nuts are located with an ordinary wrench, you may have to get a special tool called a basin wrench that will enable you to grab the nuts sideways while reaching up from below and can be adjusted to all kinds of positions.

Basin wrenches are sold in all hardware stores, and can be rented or borrowed from some. For really stubborn fittings, it may help to squirt a little penetrating oil on the connection and tap lightly with a tool handle to vibrate the fitting. Continue for about 10 or 15 seconds, then try again.