With a banner proclaiming "Water for West Texas," businessman Al Robertson set out from Lubbock, Tex., last month in an old cotton gin trailer decked out as a covered wagon. His goal: to deliver a new $809 waterbed to President Reagan.

With the help of the Waterbed Manufacturers' Association, Robertson sought to publicize the drought in the northern part of his state. But a ceremony arranged with the White House Gift Office was canceled just a few hours before the appointed time; Robertson said he was told by a member of the president's legal staff that the gift was "pure commercialism," that he was "naive" and that no gifts less than 100 years old could be accepted.

"I'm told the president simply did not want to sleep on a waterbed," said presidential press assistant Kim Hoggard, adding that White House officials weren't impressed with the "Water for West Texas" sign on his wagon because on the other side was "a waterbed promotion." The bed is in the hands of the General Services Administration; it will be offered to federal agencies as surplus property and if there are no takers, put up for auction. Robertson said he is not giving up the quest.