More than half of the 500,000 apartment units in the Washington area are heated by oil, and for their owners, getting out of the fuel oil price squeeze isn't easy.

Many area apartment buildings are old and their owners cannot afford the capital outlay needed to make them energy-efficient.

"When these apartments were built, energy costs were negligible," said Raymond Howar, a landlord and president of the Washington Board of Realtors. "We were paying four or five cents a gallon for oil. You didn'r bother about conserving energy. If you want to make these buildings energy-efficient now, you're talking about massive infusions of capital."

Frank Emmet, a Washington realtor who manages about 50 small buildings in similar straits, said contractors in the old days often installed oversize furnaces in the old buildings "to keep it hot and make everybody happy."

"We're trying to button the windows, keep the doors shut, make the tenants aware of energy conservation," said Emmet. "But these big beauties (furnaces) in the basement are cranking out (heat) at an uncontrollable rate."

Landlords are trying to conv ert many buildings from oil to gas heat, which is less expensive. Most of them won't be able to convert this winter, however, because Washington Gas Light Co. is struggling with a backlog of 5,000 new applications for service.

Most of these are for single-family residences, the easiest buildings for the gas company to convert. Converting a large apartment building can involve costly engineering and planning.

Some of the landlords are bitter about the delay. "It's outrageous that a public utility can't give you the services you need," said Howar, who has applications in for four buildings in the District and two in Virginia, only one of which he thinks will be converted this year. "It affects the tenants, because in the long run they're going to pay the additional charge (for oil over gas)."

A WGL spokesman said the company is doing its best to hook up the new customers after years of tight gas supplies and limited hookups during which the company's engineering and marketing staffs dwindled.

Now there is plenty of gas, the spokesman said, and the price is not likely to catch up with the price of oil for five years.

Emmet said he hasn't applied for gas conversion for the 50 small apartments he manages, because WGL's backlog would make that "an exercise in futility." But he added, "I don't know if the owners have the financial wherewithal to change even if they could."

Howar, the large landlord, is luckier than most because WGL has nearly completed the conversion of his largest property, the 149-unit Westmoreland Terrace apartments in Arlington.

With his oil costs up 65 percent this year, Howar figures he will save over $16,000 -- $108 per unit -- by switching to gas, even after paying $16,000 for new gas burners.

The cost of gas heat this year -- an estimated $43,510 -- will be less than the $45,800 cost of oil last year, Howar said. Oil heat at Westmoreland Terrace would have cost $75,570 this year, he estimated.

Next year, with the cost of conversion already paid off, Howar thinks he'll save even more -- over $31,000 or more than $200 per unit -- even with a possible 1.4 percent rate increase for which the gas company has applied in Virginia.

Despite these projections, Howar plans to raise rents more steeply at Westmoreland Terrace this year than he did last -- 13 percent at the expiration of leases compared with 9 percent last year. There is no rent control law in Virginia.