Members of Congress have many perquisites, but have you ever heard of a uniform allowance? Readers of the San Francisco Examiner learned of this unusual if nonexistent perk recently via Rob Morse's column.

"Bargain hunters are still grumbling about the northern California congressman who showed up last last week at Grodins' a local counterpart of Raleighs half-price sale, picked out $2,000 in clothes . . . then asked to charge half of them . . . to his federal uniform allowance," Morse wrote. "Therefore, the clerk had to call Washington for verification, which meant great delays" for those waiting behind the unidentified lawmaker.

My first reaction on reading this was incredulity. Then -- aha! -- I deduced that the clerk was calling the congressman's Washington area Visa or MasterCard creditor to see if the charge would be allowed.

Incredulity was the right reaction. Morse told me yesterday that the whole thing was a hoax, beginning to end, relayed to him by a source he once trusted. And Morse now knows that congressfolk don't have either a uniform or a uniform allowance. Just lots of other perks. Tree Pickups

Remember, Metro Scene was the first to report back in the hot and humid season that a local entrepreneur was offering great buys on Christmas cards and that holiday catalogues were arriving in the mail. Now we figure we're first in the media to report the schedule for picking up discarded Christmas trees.

The Montgomery County government has announced that the annual collection of trees will take place Saturday, Jan. 4, and Sunday, Jan. 5. That tree you haven't yet gotten around to buying, erecting and decorating may be taken either day to "any active elementary school parking lot." Just curious, but what kind of activity is required for a lot to be described as active? A Very Special Party

In this column, we wince at reporting such things as Christmas parties -- so many are held in this huge region that publicizing one leads to countless requests to report on others.

But here's an interesting case of a party being held by the owners of a downtown Washington watering hole at a location far removed from their own establishment.

For five years, Thomas Goss and Danny Marshall, who operate the Sign of the Whale on M Street NW, have solicited their customers and those of rival establishments to raise money for a party at St. John's Child Development Center on MacArthur Boulevard NW. Donors gave up to $40 apiece.

Today, St. Nick (alias Tom and Danny) will take their gifts and refreshments out to what they describe as the "very special children" -- many of them retarded and autistic -- at the St. John's Center.