Natural gas -- once the fuel of choice here for new houses -- is back after a six-year moratorium on new customers in this area. But it won't be available at the flip of a switch.

While Washington Gas Light Co. says its pleased with the customers response during its initial re-entry into the market, it plans to be cautious about expansion, largely because it will take time to gear up its dormant new-home business. First, the company acknowledges, it must gain the confidence and support of builders and potential customers -- many of whom have forgotten about natural gas.

While the president of the Metropolitan Washington Builders Association believes that half of the builders in the area are switching to gas for their new houses, not all builders are convinced and adequate supply exist. Some say that new advances in energy efficiency have diminished gas' previous cost advantage over electricity.

Last year, Washington Gas Light began increasing its 540,000-customer base by adding an initial 11,000 hookings in the metropolitan area. Another 12,000 meters were approved by regional public service commissions this year. The company hopes to expand its service to houses and businesses at a rate of 2 percent a year.

Like other U.S. natural gas companies, Washington Gas Light says it is encouraged by the dramatic improvement in gas supplies and the potential for synthetic gas production.

"We know we have the supply -- right now we have a surplus over what we're trying to sell," said WGL marketing director Fred Reckeweg. "I'm sure people have reservations about a availability. But there's not a question in my mind that we have an adequate supply."

While 3,000 new hookups have been approved for the District, only 2,000 new meters have been installed, mainly due to limited construction in the city and the difficulty of hooking up existing houses.

In Maryland, 4,200 hookups were made last year and 3,300 were commited this year.In Virginia, 2,700 houses received gas for the first time last year; 1,300 of 4,000 approved hookups have been made this year.

Reckeweg said allotments were signed up quickly last year, particularly in the faster-growing suburbs. About 100 customers finally got natural gas after waiting out the moratorium by using propane.

The marketing director said that because of "confusion" in the market and the problem of gearing up again, expansion of service will be slow. The company will first have to extend its mains, he said, and potential customers will have to be re-educated about natural gas and its availability.

Much of the reentry of gas into the market will depend on builders, who have had to construct all-electric homes here in recent years and have been concentrating on making them more energy-efficient, Reckeweg said.

"I think the public is ready for natural gas," said Spencer Stouffer, marketing vice president for the Miller and Smith home building firm. "gas has had a good reputation for so long. . . ."

A spokeman for Washington Gas Light said that it costs the owner of a typical residence here $540 to $550 a year for gas-fired heating, cooling, cooking and water heating. That is about half the comparable cost for electricity, he said.

In recent months, the gas company has been encouraging builders to use gas in new housing projects. It began placing advertisements in trade magazines two months ago.

The primary marketing targets are new housing developments, where it is easier to install pipes, Reckeweg said. The company is also converting existing houses to gas fuel if the installing the lines dosen't cost the company too much.

Reckweg said the connecting a house in the District could cost the utility $3,000, largely because of labor costs involved with breaking up concrete and digging up lawns. Where installation is difficult, customers are billed for $500, of the cost, he said.

Some builders say that older buyers of houses who are familiar with natural gas generally prefer it over electricity, but he said that many younger buyers are unfamiliar about the difference.

Some customers still worry about leaks and explosions, one builder said.But Reckeweg noted that new gas appliances don't have the familiar pilot light of the older appliances. More home fires are caused by electrical problems than by gas, he said.

Gas company officials maintain that nutural gas is easier to cook with and warms the air better than electricity -- as well as being less expensive. Fuel oil would have to drop from the currrent 72 cent a gallon to about 45 cents to complete with gas, they added. In fact, contractors report that a number of homeowners are asking to have their oil furnaces coverted to gas because of rising oil prices.

Last week Washington Gas Light asked for an 18 percent rate increase in the District, however, that would raise the average heating bill by $8.74, to $52.59.

At the same time, builders who have been building energy-efficiency into their electrically-heat houses in recent years argue that such features as heat pumps -- when augmenting electric systems -- represent a big fuel saving for buyers.

"With the more efficient heat pumps, the cost per 1,000 BTUS is less than natural gas," said builder David Miller. Hooking up to gas now would mean dealing with a second utility, he said, and already completed house designs would have to be altered. The need to additionally ventilate a house using combustible fuels adds to the heat loss, he noted.

Miller, who is not using gas in his new houses, said: "We'll always have electricity, but we could run out of gas and oil. There might be plenty in the pipelines now, but what about in 10 years?"

Lawrence Goodwin, president of United Research and Development Corp., which is putting gas into 15 town houses in Southeast Washington, noted that it is easier to put in electric lines than gas connections. Gas installations are more labor intensive, because they have to be tested for pressure and leaks, he said. "A lot of builders don't even know its available," he added. CAPTION: Picture,

Realtor Katherine Peck and her daughters say they've always done well when the market is bad. Real Estate Happenings, D4.