One of the nice things about working for the government is the steady paycheck, right? Wrong, say some Labor Department employees who are thinking about setting up a did-you- get-yours? lottery every other Wednesday, which, at one time, was known as payday.

Because of a problem -- somewhere between the Treasury Department and some people's mailboxes -- hundreds of workers who are supposed to get their paychecks by mail at the home address now find those checks delayed, from two days to as much as two weeks. Because Labor Department aides, like most other federal employees, get paid every two weeks instead of once a week, a late or missing paycheck can be doubly distressing.

Workers whose checks are sent to their banks or credit unions via electronic transfer aren't having problems. But many employees who get their checks by mail aren't getting them on time, according to the American Federation of Government Employees local at the department.

Labor officials say that the checks are properly addressed and are being mailed out promptly by the Treasury Department.

Checks for workers west of the Mississippi go out on a Saturday and those for delivery east of the Mississippi are mailed Monday. But somewhere along the line (insiders believe it may be faulty postal optical scanners), checks are going astray, with those bound for Washington ending up in Minnesota, while some checks for Kentucky field offices first going to addresses in Massachusetts.

Officials hope to have the bugs ironed out before the no-check syndrome strikes the department's new secretary, Ann McLaughlin.Don't Drink the Water

That's the word for employees at the Ariel Rios Federal Building, on 12th Street between Pennsylvania and Constitution avenues NW. A routine check several weeks ago indicated high lead content in some of the water, causing the General Services Administration to cut off all water fountains and notify workers to rely on bottled water until the problem is corrected.

One of the problems, workers say, is that there isn't enough bottled water to go around, prompting some people to bring Perrier from home.

GSA says it hopes to identify the source of the lead -- which it says doesn't come from the city water supply -- and have the fountains flowing soon.

The building houses employees of the IRS, the Bureau of Alcohol, Tobacco and Firearms and some Justice Department folks.

The ATF crew in particular is rather macho, and it doesn't want law enforcement types in other agencies to get the idea that its people are drinking imported water on the job. Part-Timers' Benefits

The Association of Part-Time Professionals has published a new handbook telling workers and employers how to prorate benefits for tax purposes, annual leave, insurance and the like.

The guide costs $18.95. For information, call Diane Rothberg at 734-7975.