Please don't make the mistake of thinking that the business of Washington is government. The business of Washington is conventions.

The Washington area played host to 860 conventions in 1985, according to the Convention & Visitors Association. These get-togethers brought more than 1 million delegates to town. The visitors spent more than $650 million while they were here, much of it on meals.

But the conventioneers didn't finish all the food they ordered. So Beverly B. Swann, director of personnel and meetings at the National Society of Professional Engineers (based in Alexandria), wonders if there isn't a way to direct those leftovers to the homeless.

"At a recent national meeting of the NSPE in Fort Worth, Tex.," Beverly writes, "NSPE arranged for unserved meals to be donated to local shelters and missions. The hotel proved very cooperative, either wrapping the meals for pickup by the service organizations or by actually delivering the meals to the facilities. All we had to do was coordinate the arrangements with the hotel and the shelters.

"I challenge local organizations to investigate the opportunity to offer such assistance . . . ."

I took up Beverly's challenge -- and ran smack into a D.C. health regulation.

It prohibits D.C. hotels from sending convention leftovers to shelters if the food has been put on a plate and served. Similar regulations are on the books in every suburb.

Hotels (and their customers) could donate unserved food. But because convention managers have become much more cost-conscious lately, there is rarely much unserved food going begging. What little there is usually gets served in the employe cafeteria, said Linda Hughes, assistant director of public relations at the Sheraton Washington Hotel.

If conventioneers can't bear not to help the homeless, there is nothing to prevent them from deliberately ordering too many meals so they'll then have a few to give away. Nor is there any way to stop a delegate from taking 314 pieces of roast beef from a platter, stuffing them into her purse and hopping a cab for a shelter.

But this is one of those situations where an apparently great idea proves undoable -- at least in a systematic, legal way. Would that it were otherwise, but it isn't, and it doesn't look as if it will be.

Latest local high school reunion plans:

Walter Johnson '66: Aug. 16 and 17. Further information: 428-3394.

Yorktown '76: Set for June. Call Lisa, 428-0876.

Washington-Lee '51: Organizing. Call Patricia Linton Norris, 893-6853.

Sherwood '25 through '35: June 4. Call Elizabeth Dunlevy, 986-1240.

Coolidge '61: June 20-21. Call Ray Rice, 842-2797.

Cardozo '46: June 21. Call Anna Jones Marsh (582-9283) or Norma L. Vincent (723-7145).

Western '66: Organizing. Call George Keys (452-1555 office, 244-4437 home) or Lois Dyer (364-3866 office, 882-7924 home).

Thomas Jefferson '76: Aug. 9. Call Paul or Mary Quigg, 378-9534.

T.C. Williams '76: July 5 and 6. Call Ann Mittauer Douglas, 671-7418.

Dunbar '66: Organizing. Call Francis X. Taylor (292-5591) or Nancy L. Brailsford (829-5900 office or 462-5923 home).

W.T. Woodson '66: June 14. Call Dale at 323-8108 or Bill at 301-721-3475.

Bethesda-Chevy Chase '66: June 7. Call Doug Hoff (657-3556 after 7 p.m.) or Martha Keator (986-7999 after 7 p.m.).

Annandale '66: June 21. Call Lee Coogle, 856-1287.

Fairfax '76. July 26. Same Coogle, same number.

Frederick Douglass '81: June 28. Same Coogle, same number.

Gwynn Park '56: May 31. Call Betsy Watson Behrens (868-4142) or Carolyn Suit Baden (579-6738).

Eastern '41: Aug. 9. Call Charlotte Caldwell,927-3303.

Bladensburg '61: June 21. Call Mrs. West, 779-6920.

Hammond '66: June 21. Call Karl Johnson (765-1118) or Janet Beverley Holloman (703-791-5782).

McLean '66: Shooting for fall. Call Jeff Cochran (703-368-1950 evenings, 703-557-7862 days).

Western '56: June 14. Call Marilyn Phillips,241-0391. Blair '66: June 20-22. Call Mark Levin (857-1143 office or 465-7322 home).

Stonewall Jackson '76: July 19. Call Debbie, 369-3253.

Spingarn '66: Aug. 8. Call Toni Hagwood Duckett (377-4719 days, 399-6913 evenings) or Maxine Holmes Jackson (275-5820 days, 249-9332 evenings).