You want to spend your weekend reading a good novel, taking a walk or seeing a movie.

Forget it.

What you should be doing, says home fix-it expert Al Ubell, is combing your house inside out for ways to cut back on heating and other energy costs.

"Just don't sit around," says Ubell, an ebullient Brooklyn builder and home inspector whose weekly home-repair spots on ABC-TV's "Good Morning America" have made him a celebrity of sorts.

It's not just a matter of saving yourself a lot of money as fuel costs keep climbing, he says with the proselytizing vigor of an evangelist, it's good for the country, too.

"The more efficiently we use our costly fuels, the stronger we are as a nation."

Tell Ubell you've got 10 thumbs and smack them all every time you pick up a hammer. No excuse.

"Everybody on the face of the earth in mechantically inclined -- men and women equally," he claims, noting that is his case "I'm super-duper-duper mechanically inclined."

He even suggests that keeping your home in good repair can "bless you with a little bit of immortality" -- as well as save you the cost of hiring somebody else to do the job.

"Have you ever changed a light switch?" he asks, and then recites a credo worthy of a master do-it-your-selfer:

"Every time you turn the light on, it's yours. Something clicks in your head. You remember you did it. It gives you a sense of self-worth."

A series of shows he did last year on energy saving led him to write (with George Merlis) "Al Ubell's Energy-Saving Guide for Homeowners" (Warner, 148 pages, $4.95 paper).

It's a how-to-do-it book without the technical jargon, he says, so that "even a school kid can find out how much money his parents can save in their home. Energy costs are out of sight," and they're not going down.

About 57 percent of your energy budget, Ubell writes, "goes toward keeping that house of yours warm and comfortable." Another 15 percent "pays for the hot water in your shower, bathtub, clothes washer or kitchen sink."

The remaining 28 percent "pays for cooking, lighting, running that toaster, the TV, the vacuum cleaner, the hair dryer and the dozens of other appliances we all depend on."

A feature of the book is an 80-item "energy-wise or energy-foolish" checklist. If you score 1,000 points, you've probably done about as much as you can to make your house energy efficient. But if you score lower -- probably the case -- you could, Ubell, says, save from 5 to as much as 75 percent of your current fuel costs by following his advice.

Although achieving a perfect score might take months or even years of weekend work -- even with professional help -- here are steps Ubell suggests you take first:

Control your heating/cooling system: "That doesn't cost you anything. For every degree you lower your thermostat in the winter, you will save about 2 to 3 percent in heating costs. A drop of 4 degrees will save you 8 to 12 percent. A drop of 5 degrees, 10 to 15 percent.

"You have to stop running around the house naked. Wear a bathrobe and slippers in the morning. If you wear a light sweater, you can lower the temperature 1 degree."

Insulate: "Proper insulation can save 20 to 40 percent of your home-heating bill in the winter and about 10 to 15 percent of your cost for home cooling in the summer."

Among areas to be insulated: "Ceilings with cold spaces above. Exterior walls. Walls between living space and unheated garage or storage rooms. Floors above cold spaces -- vented crawlspaces, garages, open porches and any portion of a floor in a room that extends beyond the wall below."

Install storm windows: If they are well-fitted, "You should be able to cut your heating bill by 20 percent."

If you can't afford the total cost of $25 to $70 or more per window, "Buy windows for the north side of the house first. Then next year the west. Then the east. The last on the south side."

If you're using the air-conditioner in the summer, "Those storm windows you installed to keep out the stiff winter winds can keep the cool, air-conditional breezes inside during the summer."

Caulk and weatherstrip: A well-caulked house -- "around window frames, wherever two different materials or parts of the house join" -- should cost "about 10 percent less to heat." Anybody can do it, says Ubell. "You just squeeze this goop out into the corners."

Weatherstripping doors and windows "wil probably save you 10 percent of your home heating bill every year from now on."

Have your heating system serviced regularly: Increasing its efficiency could save you 30 percent. If it's a gas-fueled system, "Get it cleaned at least once a year. If it uses oil, make it twice a year."

There is an "inherent conflict of interest," he suggests, if the firm that sells you the oil also does the servicing. "His business is selling oil. It's not in his interest to reduce your consumption."

Ubell, 47, built his own home in Brooklyn 20 years ago, practicing most of what he now preaches. "I put in the best insulation money could buy, and it keeps on benefiting me."

The average heating cost (gas) for his home -- "quite large" -- is "$1,100 to $1,200 a year." But if he hadn't insulated so well, he estimates it would be at least "$1,800 to $1,900."

Fuel that we waste, "is less fuel we'll have for the kids of tomorrow."