Cold. That's what it was in the Washington area yesterday, about 10 degrees on the wind-chill index at mid-afternoon. Bone-numbing, nose-running, freezing cold.

There was the predictable winter fare: Boilers broke down, waterlines ruptured and heating oil tanks went dry. More than 100 D.C. residents, shivering beneath blankets in heatless apartments, appealed to the city for help.

Several schools closed, but Timothy Williams, 10, and James Thomas, 11, didn't mind a bit. Their school, Young Elementary in Northeast Washington, was locked up tight. The boiler that supplies heat to Young, Spingarn High School, Phelps Vocational School and Brown Junior High was down, too, for the fourth day in a row.

So Timothy and James were the only ones around. They were on the hill out in front of Young, cascading down the white-covered slope on make-shift cardboard sleds, whooping and hollering and having a good time.

"It's like another vacation," said Timothy. "Don't make no difference why."

But for hundreds of others in the city, it did make a difference. It's one thing to be outside in the cold when you want to be, quite another to be stuck inside in the cold. Numerous tenants throughout the city, both in public housing and private apartment buildings, have complained in recent days that their buildings have been without heat. In most instances, the necessary repairs have been made and the heat turned on again within hours, but not always.

The problem, aside from the cold weather, said John T. O'Neill, executive vice president of the Apartment and Office Building Association, which represents the owners and operators of 50 percent of the apartment space and 75 percent of the office space in the Washington area, "is that the average building in D.C is 40 years old.

"Their heating systems are old and tired.When there are extreme temperatures, the system is cranking at maximum output and things break down. Transmission lines freeze, motors die," said O'Neill.

In addition, heating experts say, heating systems are only designed to heat a building so much. "If it is 30 degrees outside, sure the system can warm a room to 70 or 80 degrees. If it is 10 degrees, the system just can't work that hard without breaking down. You get the same thing in the summer with air conditioning," one heating engineer said.

Another problem, O'Neill said, is that many of the owners of the older, smaller buildings are in such "dire ecomomic straits that oil companies have them on a COD basis. If they don't have the cash to pay for oil, they just can't get any.

"We have inflation, eight years of rent control, a significasnt number of tenants in the city who don't pay their monthly rent. If the owner doesn't have all his tenants paying rent, he can be short of the money to buy oil," O'Neill said. "I don't think anyone in his right mind is deliberately withholding heat from a tenant in this kind of weather."

Since 1972, O'Neill noted, No. 2 heating oil, the variety used in all private buildings, has risen from about 11 cents a gallon to $1.16. He said a 42-unit apartment building uses about $5,000 worth of oil a week.

Thomas Butler, a city housing official, said his office has been averaging between 100 and 125 complaints about lack of heating from apartment dwellers each day for the last week.

In the case of privately owned buildings, Butler sends an inspector to the building who, in turn, issues a citation to the owner. If the owner cannot or will not restore the heat, Butler's department hires a contractor to fix mechanical problems or pays for more fuel oil. The District also places a tax lien against the property and imposes a small interst charge until the city is reimbursed.

If the lack-of-heat violations are recurrent or flagrant, Butler said, the case is turned over to the D.C. Corporation Counsel's office, which brings charges against the landlord in Superior Court. If found guilty, the landlord can be fined from $10 to $300 per day for each violation.

If the problem is with a city-owned property, the onus falls upon the Department of Housing and Community Development's property management division to make the repairs.

The four schools in the Spingarn complex were intitally closed Monday when contractors were late delivering fuel oil, acording to David Huie, a school system maintenance official. When that problem was taken care of, the said the sump pumps in Spingarn's sub-basement boiler room -- which supplies heat for the other three schools in the complex -- malfunctioned, and the boilers once more had to be turned off.

"The problem," said Huie, "is when the plant shuts down, you can't just turn the switch and bring it back up immediately. We're getting ready to crank Spingarn up again, but it will take some time to get it warm again."

The biggest problem, however, is still the weather. The National Weather Service is calling for highs today in the upper 20s, with lows in the teens and a chance of snow today and tonight. Tomorrow's temperatures are expected to be in the same range, though stronger winds will chill the area considerably more.

It could be worse. Yesterday's official low of 17 wasn't even close to a record. In 1878, the temperature dipped to zero. And they didn't even compute wind-chill factors then.