Rrrrrrrrrrrr, sput, sput, Rrrrrrrrrrrr, chugka, chugka. . . .

The stair-climbing grocery cart stalls for a second then whines like a consumptive Cuisinart, its motor coughing back to life.

"We don't have time to get a lot of the bugs out," says the bespectacled professor in his brown-plaid sport coat and orange-striped shirt.

The stair-climbing grocery cart probably will never be marketed by Popeil or Ronco or any other late-night television entrepreneur. Nor will the mechanical page turner for piano players, the automatic pet and plant tender that feeds Fido and waters the philodendron for two weeks, the solar-powered refrigerator, or the solar carport.

The same goes for the antitheft bicycle with an exploding smoke bomb under the seat, and the fallen-person lift: an inflatable whoopee-cushion chair for elderly persons who cannot get up by themselves after a fall.

"It works neat," says Dr. Clifford Sayre, "though I'll admit we never tried it on an incapacitated person." The chair, he said, was originally designed to come and find the fallen person. "But we found that impractical." d

Sayre teaches a course at the University of Maryland called Mechanical Engineering Systems Design. The inventions -- some would call them Rube Goldbergs -- are the senior engineering students' final exams.

Surrounded by his youthful Leonardo da Vincis, Sayre demonstrated the gadgets and gizmos destined for instant obscurity.

"Now this is the mechanical page turner for piano players. It's quite a problem, you know."

Larry Gotts sits in front of a bulky aluminum stand that holds the piano music. Attached to the top right-hand corner of each sheet of music is a paper clip. Gotts presses a button. A long thin arm, with a magnet on the end, swings over in front of the music, grabs the corner paper clip and turns the pages. Eureka!

"We're looking to patent it," Gotts said. "Right now, 3,000 patents exist for page turners. We think we've got the best one."

There is only one hitch. The students have yet to invent a gadget to paper-clip thousands of pages of piano music.

What happens if the turner goes berserk, willy-nilly turning pages at breakneck speed?

"You've heard of the minute waltz," Gotts deadpans.

Moving to the basement machine shop, the class demonstrates the plant and pet tender. Made of polyvinylchloride tubing, the contraption has shelves for plants and hooks up to a water faucet by a garden hose. Every five days, an electonic timer releases two minutes of water that runs down a thin hose attached to each plant.

A separate gizmo, a cross between an aluminum silo and a spaceship, releases dry dog food in premeasured amounts.

The piece de resistance, however, is the stair-climbing grocery cart -- a 20th century marvel that could revolutionize the way we lug our foodstuffs home.

There's only one problem: the cart weighs about 30 pounds.

"It's more awkward than we thought," said Greg Moores. However, there's no danger of the climbing cart running amok, leaving broken eggs and spilled milk behind. "It has brakes," he said.

Upcoming projects for next semester include a street-cleaning device for the countryside, Sayre said, adding, "You know, those roads have gullies on both sides, and normal street cleaners don't do the job."

What he has in mind is a flexible device with a scoop on the end to pick up the debris in the gullies.

"So far," he said, "nobody's taken me up on that, I don't know why."

The class' only failure in its three-year history, Sayre said, was a project proposed by a local sports-equipment dealer who wanted the engineering students to come up with a scheme for marketing wooden tennis paddles. Instead, the kids invented a way to make the paddles stronger.

"He didn't like that," Sayre said.