SPRING is the season for roof leaks, which are usually caused by rain penetrating roofing damaged by winter weather. At the first sign of a leak, often a wet spot on the ceiling near the corner of a wall, go to the attic, if possible, and find the spot where the water is dripping.

Catch drips in a pan or other container while you mop up water on the floor or joists. Remove wet insulation, as it will have to be replaced; if it remains, it can expedite the rotting of wood.

Spread plastic sheeting beneath the leak and place the container on that. Monitor the area until the rain stops and the roof dries. Only then can repairs be made.

If you cannot get to the attic, drain the leak from below by drilling in the wet spot holes about a quarter-inch in diameter. That is to keep the leak from spreading. Three or four holes should drain a six-inch spot.

Catch the water in a container. If insulation is above the ceiling, replacing it may involve removing part of the ceiling, which will have to be patched and repainted.

Once the leak is under control, the next step is finding its source. Water can travel in several directions and for some distance over rafters and other framing. If the attic is finished so that the rafters are not visible, or if there is no attic, you can find the source of a leak only by inspecting the exterior of the roof. If the roof rafters are visible in the attic, inspect them and the sheathing above them with a flashlight. Follow any trails of moisture upward to where they begin.

Also examine areas near the chimney and plumbing vent, where dormers project or where roof sections join at angles to each other. All these places are usually protected by exterior metal flashing. But if the flashing has deteriorated or is improperly installed, water may penetrate it or trickle past faulty seams.

On finding where a leak appears underneath the roof, measure from it to some object that is visible both inside and outside the house like the chimney or a dormer. To find the spot, climb onto the roof and measure from the object the same distance along the roof.

Begin searching for the source of the leak from that point. Because water cannot flow uphill, you need not look between the point and the lower edges of the roof.

Hunt above the point as far as the roof ridge and several feet to each side. Look for curled, torn or missing shingles, opened seams, cracks and rust spots in flat, roll or metal roofing, and corroded or deteriorated flashing. With flashing, also inspect for open seams.

Nearly all leaks can be patched without replacing the damaged roofing material; naturally, missing shingles must be replaced.

To patch curled shingles, brush away debris and liberally apply plastic or asphalt roofing cement to the underside of the shingle and the roof area. Press the shingle flat and weight it, if necessary, with two or three bricks until the cement hardens. Do this on a day when heat from the sun makes the shingle flexible; otherwise, flattening may break it. Opened seams in flat and rolled roofing can be patched the same way. But to patch cracks and broken blisters, use general-purpose reinforcing membrane, an asphalt-saturated cotton fabric.

With blisters, make an X-shaped slit in the roofing and spread the flaps to let the area dry. Afterward, force roofing cement beneath the flaps and then press them flat.

Spread more roofing cement over the repair and press a piece of membrane into it, making sure it is completely embedded. The membrane should extend about two inches beyond the damage on all sides. With cracks, only spreading cement and embedding membrane are necessary.

Finish both repairs by troweling a layer of cement at least an eighth of an inch thick over the membrane and several inches beyond it. Smooth the cement so that there are no ridges to collect water.

Reinforcing membrane and roofing cement can also be used to patch metal roofs, but the rusted metal have to be removed and the area treated first. Pry up any split or blistered roof coating to expose the bare metal. Scrape away all flaking rust and chips with a wire brush and then apply rust converter, which hardens rusty metal and prevents future rust. After the converter dries, cover the spot with roofing cement and membrane.

To patch a torn or damaged asphalt shingle, cut a piece of metal flashing or spare aluminum siding to a rectangle large enough to cover it and extend three inches beneath the shingles on each side. Carefully raise the damaged shingle and spread roofing cement liberally underneath.

Coat the underside of the metal and slide it into place beneath the raised shingle and beneath the edges of the shingles on both sides. Then spread cement on top of the metal and press all of the overlapping shingles, including the damaged one, down on top. Weight the shingles until the cement hardens.

Patch small holes in flashing by covering them with roofing cement. On large areas, use reinforcing membrane and cement.