IT WAS 7:15 in the morning, the temperature was well below freezing and the wind was whipping ferociously down the streets of Reston.

"I wonder," the man said to his four companions huddled at the Colonial Transit bus stop, "whether the bus is just late again, or whether they have decided to scrub it again."

Such questions are asked at bus stops across America every day, but in the case of Reston's once-glorious commuter bus service to downtown Washington, they are unusually pertinent.

The fact is that privately owned Colonial Transit misses, on average, six of its scheduled 39 runs from Reston every day and sometimes more than that. On Jan. 3, Colonial Transit buses missed 11 inbound runs to Washington and two of the buses that did run broke down en route.In the evening, 15 outbound runs -- almost half the schedule -- were missed.

"I suspect that what they do," said Kirby Lamar, a regular rider from Reston to the Pentagon, "Is spread around the shortage. The bus that is most convenient for me seems to run only about four out of five days."

Lamar's suspicion is correct.

"We do try to spread the failures around," said Colonial president Gary Penn. "We try not to miss the same run every day."

If Colonial Transit suddenly went out of business, however, 5,500 Northern Virginia commuters to Washington or the Pentagon, including about 1,300 from Reston, would have to find a new way to get to work.

The newest of Colonial's buses is at least 12 years old; the oldest is 24. The transmissions clank or lock in second gear. Windows are cracked and dirty.

Some buses belch oily black smoke. The doors don't always close all the way. The reading lights are undependable. Many buses have made runs without heating this winter; summers, the air conditioning never works.

Penn, who occasionally helps out as a mechanic, said that he will not put an unsafe bus on the road. But the federal Bureau of Motor Carrier Safety has fined Colonial once for operating unsafe equipment and is investigating a second round of safety complaints. Full inspections of all of Colonial's 140 or so buses are scheduled.

Penn has been Colonial's president and co-owner for about two years. He is frank about the problems: "We have ancient equipment, no facilities, salftaught personnel. You can't expect us to turn it around in two years. My goal is to turn it around in five years."

Colonial opened its first Washingtonarea garage in December, a five-bay facility near Dumfries.Before that all heavy maintenance had to be done in Fredericksburg, almost 60 miles from Washington. Minor repairs to Reston buses are still made in an open field near Dulles Airport while Penn awaits final zoning approval from Loudoun County for a garage there.

"The problem," Penn said, "is that once we bought the company, the riders expected air conditioning and new buses. But they don't want to pay for it; we really got roasted in public hearings" after Colonial applied for a 27 percent fare increase from Prince William County points to Washington.

Colonial buys only used buses and it must do so out of profits. Public transit authorities such as Metro pay only 20 cents on the dollar for a new bus.The rest comes from the federal government. Colonial has no federal subsidy.

In addition to the Reston service, Colonial provides regular commuter runs to Washington from Fredericksburg, Dale City, Triangle, Dumfries and Woodbridge. Riders from all locations share in Colonial's problems. "It's the same equipment," Penn said. An Unhappy Marriage

THE RESTON riders are the best organized, however. They trace their roots to the beginnings of the Fairfax County new town more than a decade ago, when some of the Reston founders contracted to hire one bus from the old WV & M Coach Co. to take them to work in Washington. n When WV & M became one of the four privately owned bus companies that were folded into Metrobus in 1973, Metro picked up the Reston service. It was an unhappy marriage.

Reston Commuter Bus (RCB), a nonprofit corporation formed by Reston residents to charter and administer the bus system, was expecting price cuts because of public ownership. Metro's board members, who inherited skeletal bus companies with no spare arts, deteriorating equipment and expensive labor contracts, found they needed subsidies to keep Metro service afloat. D.C. and Maryland members could find no reason to subsidize specialized service just for Reston.

Metrol began to bill RCB for costs based on a new formula. The price per bus run rose from $40 to $57.08 in early 1974, then to $66.91 in late 1974. RCB was forced to raise its fares from $1.20 to $1.50, and even received some subsidy from the Fairfax County government.

Colonial became the answer. It contracted to provide buses, albeit old ones, to RCB for $50 per trip. Fares were kept at $1.50, where they remain today. Metro fought the change before the Washington Metropolitan Area Transit Commission, but lost. Reston celebrated. The Metro giant had been slain. In October 1975, Colonial began to assume the Reston service.

"For the first year the service was quite good," said passenger Lamar.

There was a steady deterioration from that first year, however, until last August. "August," said Colonial president Penn, "was the pits."

According to Pnn, Colonial's nonunion drivers staged a slowdown after the firm's dispatching system was reformed. At the same time, age and lack of maintenance facilities caught up with much of the equipment.

There was improvement from August until the cold weather began. Diesel engines do not loke cold weather and must be warmed up. Air brakes function poorly in cold weather, particularly if there is water in the air lines. Water frequently collects in Colonial's decrepit air lines.

"We were not properly winterized," said Charles Kenny, Colonial's director of operations.

Lamar points to other problems. "Yesterday, the driver had to stop the bus four times. There was a mechanic on board. He would get out, do something in the back of the bus, then we would take off again."

Colonial has some economic advantages over public transit systems. A part-time driver picks up the bus in the morning, drives a load of people to work, and parks the bus at the Pentagon free during the day. Then he drives it back in the evening, with a full load. No profit-destroying empty runs; no drivers being paid for eight-hour days when they work only four.

Penn said his company is financially viable. In 1978, he said, revenues were about $3.5 million and "gross profit before taxes was $100,000 plus, and I took a modest salary."

"when we started having service problems," said RCB president Jack Price, "we looked at alternatives. There wasn't one other bus company that had an interest or desire in the Reston service."

Some members of the RCB board have been quietly talking to Metro officials once again to see if maybe... Iran and Reston

ON THE COLD morning that started this story, the bus did show up, 11 minutes late. The man who had wondered out loud whether it ever would offered this comment as the bus luched along:

"You know, in Iran, illiterate people burn the buses. Here in Reston, people who would go to an administrative law judge if somebody moved a water cooler 10 feet will put up with something like this."