If nothing else good came out of yesterday's partial shutdown of the federal establishment, at least you found out whether or not you are an ITTOSOAO.

If, for example, the boss told you to put on your coat and go home, that means you are not an ITTOSOAO.

If, on the other hand, your chief told you to stick around and lock up the nuclear weapons, secure the office petty cash fund, close the venetian blinds or hide the top-secret files, that makes you an ITTOSOAO. The initials stand for a person who is performing duties that are "Incident To The Orderly Shutdown Of Agency Operations."

About half of metro Washington's 360,000-plus federal workers, according to one rough estimate by an Office of Management and Budget official, were sent home yesterday because their agencies ran out of money at midnight Friday and President Reagan vetoed a stopgap funding bill that had cleared the Senate and House over the weekend.

Most of the area's 90,000 Defense Department aides stayed on the job, as did law enforcement, tax collection, medical and other "essential" personnel. But the lines got blurry because of the confusion. In some agencies bosses were told to clear out 60 percent of their staffers, regardless of jobs, as soon as possible. The White House shut down its "comments" telephone line perhaps to let irate or supportive callers know the White House was itself biting the bullet. But many White House aides were asked to volunteer to work, and they did.

An Education Department worker, who was told to go home, called her sisters at the Labor Department and Veterans Administration to see if they wanted a ride? Both said they had been told to keep working. She can't understand why her two sisters are "essential" or are ITTOSOAO's, and she isn't. Not many people can understand what happened yesterday.

Despite the confusion, most important benefits were unaffected by yesterday's doings:

Insurance: As pointed out in the Nov. 6 column that dealt with benefits during furlough, enrollment in health and life insurance programs remains in effect . . . You earn credit for annual leave and retirement while on any furlough as long as it doesn't last over six months.

Leave: If you were on previously approved annual leave you will be paid for yesterday, even if your coworkers who were on the job and sent home get paid only for time worked. Obviously you cannot ask for annual leave once a furlough begins.

Executive Pay Raise: Rep. Mike Barnes (D-Md.) says the raises are still possible. Congress may try again next month. Details tomorrow.