Jimmy Carter may be commander in chief, leader of the Democratic Party, head of the government and President of the United States, but when it snows here Hugh A. Carter Jr. becomes the most important man in Washington.

Hugh Carter, the President's cousin, is the newly designated official who controls the panic button that is pushed when the nation's capital is terrorized by real winter.

It will be up to Carter (Hugh, not Jimmy) to decide when, and if, the area's 347,000 federal workers go home early or; if it snows during the night, whether they can come in late because of hazardous weather conditions.

Our government has a plan for everything, whether it be survival after a nuclear attack or snow hitting Washington.

The master plan for coping with snow in this federal city is, in some ways, more difficult than contingencies for saving the rest of the world. That is because while the seat of government is here, so many key bureaucrats and officials live a long way from their respective offices. Some believe it is easier to airlift a battalion of paratroopers overseas than to cope with the chaos that snow brings to this city.

The master plan for coping with winter problems has been revised and updated as of Nov. 30. The plan is called: "Communications Procedures For Control Of Employee Dismissals, Agency Closings, And Leave Treatment During Emergency Situations In Washington, D.C."

This is how the procedure works:

1) First, it has to snow.

2) The D.C. Department of Transportation monitors both weather and traffic conditions for the city. When trings start to get hairy, they contact the Interagency Advisory Group. The IAG is based at the Civil Service Commission, and made up of key federal personnel directors.

3) If the D.C. government agency decides that the weather or traffic conditions are bad enough they so advise the mayor.

4) The mayor then calls the IAG.

5) The IAG then calls the chairman of the Civil Service Commission and the executive director.

6) The chairman or the executive director then calls Hugh Carter.

7) Hugh Carter says go, or no go.

8) If it is "go" the procedure is reversed. The IAG starts telephoning various federal agencies telling them when to send people home. This is all done (at least it is supposed to work this way) based on bus and Metro schedule changes.

The problem is, of course, that when the snow starts to fall all the telephone lines in Washington are busy. People call home to ask if it is snowing there; car pool members call to discuss the weather, and everybody calls radio, TV and newspaper friends to find out if they have heard anything. They usually have not, because their telephone lines are busy.

In that case, federal agencies used the Defense Coordination Tele-Typewriter Network (DEFCORD). It is run by the General Services Administration and is used in emergency situations to bypass regular telephone lines.

If it snows during the night, federal officials huddle early in the morning to determine if employees may come in late, in hopes of staggering rush hour traffic. That word usually gets to most people here via radio or television.

One final word. All this was prompted by yesterday's warnings that Washington might be hit by a snowfall Thursday night or Friday morning. When asked to comment, a White House spokesman said: It isn't going to snow much anyhow!"