There were 2 inches of snow on the ground at National Airport at 4:15 Friday morning when the telephone rang in the home of Patrick Korten, a senior official of the Office of Personnel Management and one of the people who helped decide whether 342,000 federal employes should come to work.

It was Bernard J. O'Donnell, deputy director of the District of Columbia's Department of Transportation. As Korten remembers it, "He said he expected between 10 and 13 inches of snow . . . . He said so far the road crews were keeping up with it and how well they would go during the day . . . depended on how the storm played itself out."

As O'Donnell remembers the conversation, "I said that we had several inches on the ground. Conditions were difficult but I thought people could come in. But if the snow fell as forecast, we'd have a lot of problems by noon. I felt on the basis of the forecast that people shouldn't come in."

That phone call began six hours of making and unmaking decisions at the OPM, which called workers in at 6 a.m. and began sending them home at 11 a.m.

OPM's about-face meant that thousands of federal employes spent two hours or more getting to work in a near-blizzard, only to be told to turn around and go home shortly after they arrived.

By the time the last workers were sent home at 1 p.m., between 8 and 11 inches had fallen in the Washington area, the temperature had dropped to 21 degrees--3 degrees below the temperature at which salt is no longer effective in melting ice--and the snow was falling at the rate of 2 inches an hour.

Buses were almost nonexistent, Metrorail service to Maryland and Virginia was severely curtailed, side streets were impassable and traffic jams kept major arteries such as I-66 jammed until well after dark.

The decision to call workers in yesterday was easier, OPM officials said: they checked with local governments and weather forecasters and decided Sunday afternoon to call workers in, while allowing "liberal leave" policies to compensate for the predictable traffic snarls.

Here is a chronology of Friday's decision offered by Korten, OPM spokesman Mark Tapscott and National Weather Service forecaster Brian Smith:

At 4:15 a.m., O'Donnell called Korten.

About 4:25 a.m., Korten called the National Weather Service. The forecast called for a foot of snow.

From 4:30 to 5:30 a.m., Korten and Tapscott called local transportation and police departments. "We found out that in Virginia, Maryland and the District the roads were beginning to accumulate snow but they were passable," said Tapscott. " . . . It appeared at the time we made the decision it would not intensify until later in the afternoon."

At 6 a.m., OPM Director Donald J. Devine was briefed by Korten, checked with the White House and called workers in under the "liberal leave" policy.

At 7 a.m., "the snowfall was progressing pretty evenly," said Smith, of the National Weather Service. Area governments reported that 4 to 7 inches had accumulated.

At 7:30 a.m., "the roof caved in," said Tapscott. "The snow was coming down pretty substantially. [But] you can't have traffic inflow into the District and then just announce, 'Okay, everybody go home.' "

At 10 a.m., the forecast changed to warn of "near-blizzard conditions," 12 to 18 inches forecast by nightfall. Metro officials called OPM to say that bus service was crippled because road crews couldn't keep up.

"The straw that broke the camel's back was when they said Metrorail above ground would shut down about 4," Korten said.

At 10:45 a.m., Devine issued his dismissal schedule. Employes at four large agencies left at 11; those at 50 small ones were kept until 1 p.m.

"Yes, we're getting a lot of nasty phone calls," said Korten yesterday. "You know, when we have a partial shutdown because of appropriations [lapses], there are always a certain number of employes who say they do essential work. They're essential--until it snows."