When a fat typist dances the jig, he poses no threat to the Bolshoi. A threat to the floor supports might be more like it.

But as we come to the end of the second week of our annual fund-raising campaign on behalf of Children's Hospital, Levey is making the concrete beneath his feet tremble. He's in Jig Mode, as the computer people would say. The reason is the money you wonderful readers are sending in.

Here are the jig-inducing Week Two numbers:

Grand Total to Date: $53,739.80.

Total Given This Week: $25,764.44.

Group Donors to Date: 133.

Individual Donors to Date: 665.

By way of comparison, that's the second-best Week Two grand total this drive has ever turned in, and it's nearly $17,000 ahead of where we were at the same time a year ago.

Does this outbreak of bucks foreshadow a record finish? Let's just say it doesn't hurt.

But like jigs, fund-raising campaigns can run out of steam. Readers can have all the sympathy in the world for the cause, but not enough to spur them toward their checkbooks. Or these same readers can read of Week Two good news and decide that they don't need to give because so many other readers are filling up the treasury.

Please don't coast. Please don't leave it to others. We have depended on readers just like you for 39 years. We still do. We always will.

Every donation is important, of whatever size. Every donation helps sick kids whose families are too poor to pay medical bills. Is there a better reason to separate yourself from a few dollars?

Help us dance a jig at the end of the 1987-'88 campaign that will threaten the walls as well as the people on the floor below. Here's how:

TO CONTRIBUTE TO THE CAMPAIGN:

Make a check or money order payable to Children's Hospital and mail it to Bob Levey, The Washington Post, Washington, D.C., 20071.

For the first time, we have Co-Donors of the Week. They are united in two ways: Their dedication to the Children's cause, and their renunciation of junk food.

Elizabeth Wilson of Fairfax weighs in with a $3 donation. "I know it's not much," she writes, "but enclosed is my McDonald's money for this week."

Meanwhile, Edward Charlton of Seabrook sent in a check for $164.25. He explains it this way:

"For 1988, I anticipate eliminating M & M's from my diet. At 45 cents per pack for 365 days, this amounts to $164.25."

Elizabeth and Edward will be a lot healthier because of their new diets, and some sick kids will be, too. Many thanks to you two calorie-avoiders. As for the rest of you with well-entrenched munchie habits, are you getting the hint?