Roscoe L. Egger Jr., the U.S. commissioner of internal revenue, has sent most of us his annual greeting in the form of a Form 1040 income tax form and packet bearing an RSVP date of April 15. While pondering it gingerly over the weekend, we encountered this engaging part of Egger's front-cover message:

"Quite often we receive inquiries about how people may make voluntary contributions to reduce the public debt. If you should wish to contribute, just enclose . . . a separate check made payable to 'Bureau of the Public Debt.' Subject to the limitations on charitable contributions, you can deduct this contribution on next year's tax return . . . . "

Gee. And it isn't even a member of the United Way.

We got to wondering about Egger's suggestion, and called up Bob Levine, whose duties as a Treasury Department public affairs officer include being spokesman for the Bureau of the Public Debt. How many people, we asked, have taken advantage of Egger's cheery suggestion?

No such number is available, Levine said, although he said he gets inquiries "from time to time--I don't know how many , maybe one a month or so."

But in dollar terms, the number is quantifiable: $220,170.87 in the 1982 fiscal year. Compared with a national debt of $1.2 trillion, that's not even a drop in the bucket.