Agriculture Secretary Bob Bergland didn't make it to work yesterday. Neither did Patricia Roberts Harris, secretary of Housing and Urban Development. Nor did Transportation Secretary Brock Adams.

But H. A. Shacklette, a security guard who said he has missed only three days work since 1963, was at his post at the Cannon House Office Building bright and early.

"It never occurred to me not to come," he said."I'm proud of my work, and I consider myself essential."

Who is essential? Who is critical to keep the wheels of the democracy turning? That was the identity crisis official Washington struggled with yesterday after someone deep in the bowels of the bureaucracy declared "Condition 3."

No one knew quite what Condition 3 meant, except that it was a rarely used code signaling that only "essential personnel" needed to report to work in the snow.

Some government workers knew by instinct that they were essential: those who keep heat, light and water flowing to ouildings; the security guards who keep bombs and vandals out, those Defense and State Department workers whose turf is in a state of crisis -- this week, for example, the Iranian desk at the State Department.

But for most of the other 300,000 government workers in Washington, Condition 3 prompted a good deal of deep soul-searching. "I heard Code 3 on the radio and I had to come to work to prove that I'm essential," joked Interior Secretary Cecil D. Andrus. "It was self-defense. I wanted everyone to know that I'm critically needed."

"I never heard of a Code 3 before," said Robert S. Strauss, President Carter's special trade representative. "But it's a hellava idea. I'm going to decide to give one to myself one of these days and take a day off."

Strauss was at his office "a little bit late" -- 8 a.m. yesterday, and working. "Of course, I think I'm essential," he said. "Everyone here is. Even if we aren't essential, we have a lot of work to do here."

Department of Health, Education and Welfare supervisor Lon Muller had to make a fast decision at 6 a.m. yesterday when an employe, Susan Aldrich, called him. She wanted to know if their health project was important enough for her to make a three-hour train trip from Charlottesville, Va. He said yes.

But by mid-afternoon, Muller was putting on his skis to go back home and Aldrich was casting about for a way back to Charlottesville. "Well, we had some very important work to do," Muller said ruefully. "But we found out that we can't do it very well when there's no one there to do it with."

At the State Department, pristine drifts of snow covered the steps to most entrances. Inside, the long corridors generally were silent and dark. Secretary of State Cyrus Vance was in at 7:10 a.m., according to his personal assistant, Elva Morgan, who struggled in a couple hours later. "I guess that means I'm essential," she said.

Down another darkened corridor, Anita Mueller, a secretary, was hard at work in the Office of Policy Planning. "I came because, well, I had a lot of work to do, and because I live close enough to walk in, "she explained.

Under Condition 3, "one defines oneself," Mueller's supervisor said tersely, handing her a stack of papers.

The Voice of America "defined" itself as essential, and continued its round-the-clock radio broadcast in 37 languages without interruption. But it wasn't easy, according to Joseph Valentine, who had walked for three hours to get to work on Monday, then spent Monday night in a downtown motel. Other slept on couohes in their offices.

"It's been a tremendous effort," Valentine said.

But much of the State Department apparently defined itself as nonessential. While there was some activity in "hotspot" offices, like the Iranian and Afghanistan desks, most other precincts apparently considered themselves safe for the day. At 2:30 p.m. the Central Africa and India offices were deserted.

Nine of the 12 cabinet officers were in their offices yesterday, although several including Energy Secretary James R. Schlesinger, Commerce Secretary juanita Kreps, who had to fly in from North Carolina, and Attorney General Griffin Bell, who had to wait 22 hours for a plane out of Atlanta, were late arrivals.

An aide to Bergland said the agriculture secretary, who has been the object of attacks from protesting farmers for two weeks, was snowbound at home.

Who is running the department?

"Nobody," the aide anwered. "It's closed."

A recorded message came on the line when calls were placed to the office of HUD Secretary Harris.

"Secretary Harris' office is closed due to the snow emergency, and it will reopen at 8:45 a.m. Wednesday" the message said.

Defense Secretary Harold Brown, a workaholic, was in at 6:35 a.m., according to his chief receptionist, Joan Bennett. "That's his normal time," she said. "He's always here at his desk at 6:35."

Attorney General Bell and Interior Secretary Andrus were answering their own phones. "We got in the office at 11:45 from Atlanta and there wasn't a soul in the office. No secretaries. No receptionists. Nobody," said Bell's assistant Terrence B. Adamson. "I suspect there are others in the building. We just haven't seen them."

"Judge Bell just asked me why we can't get the snow out of the courtyard," he added. "I'm trying to get that taken care of now."

At the headquarters of the Office of Personnel Management, where "Condition 3" is officially declared, only three people were at work yesterday, according to public affairs spokesman Robert Woodrum, "Scotty (Alan K.) Campbell (the director of the agency), Jule Sugarman (assistant director) and me."