Next time a senator or congressman is looking for that perfect constituent Christmas gift, he may need look no farther than the Rainwater Concrete landfill in Lorton.

That's right, a dump.

Hunter Price, an Alexandria postman, was disposing of shrubbery at the landfill near Engleside recently when he found nine unopened cardboard boxes marked "U.S. Government Printing Office" and addressed to the House of Representatives. Each box contained 200 manila envelopes, sized 14 1/2 by 18 inches.

Near the boxes, Price also found hundreds of l982-83 two-year House calendars--fine, blue-bordered, cardboard calendars featuring a glossy color photograph of the Capitol. The calendars, Price found, fit neatly into the heavy envelopes.

Price was indignant. "I'm just an average John Brown citizen," he said, "but I know waste when I see it and this just ticks me off. I paid a helluva lot of taxes last year."

Just how the envelopes and calendars wound up in the dump is a mystery.

Each member of Congress may order up to 2,500 of the calendar-envelope combinations from the clerk of the House. They are generally given away to constituents as good-will gestures.

The GPO said the envelopes and calendars had been shipped to the clerk of the House. The office of the clerk said 154,745 of the calendars and envelopes were distributed to congressional offices. After that, the individual boxes are impossible to trace, said Thomas E. Ladd, assistant to the clerk of the House.

"I can tell you one thing," Ladd said. "We do not destroy any excess l982-83 calendars. We would never dump any of our documents or papers." He said the calendars and envelopes might have been stolen. Often, he said, they are left in the corridors to avoid cluttering congressional offices.

Price estimates that he saw nearly 2,000 calendars and the same number of envelopes. At the $1.03 price paid for each calendar-envelope ensemble, that's about $2,000 down the drain--or the dump.