Tom Baker of Richmond piloted Deepwater Too to the day's highest average speed and led Grand Prix International class qualifiers at the halfway point of the President's Cup Regatta races yesterday in the Potomac off Hains Point.

Baker guided his supercharged Chevy-powered boat to an average of 92.30 miles per hour, almost 11 mph faster than No. 2 qualifier Robert Newman of Loveland, Ohio, in Hustler over the five-mile course.

Last year's winning average in the GPI class was four mph slower than Baker's yesterday. Speeds in other classes also were slightly improved yesterday.

Several American Power Boat Association officials attributed that to the new layout of the Hains Point course, whose 1 2/3-mile laps enable drivers to maintain higher speeds because the turns are more rounded.

Several GPI boats, including 1978 national point champion Long Gone, experieced problems breaking in new engines on the first stop of this season's APBA tour.

"It's embarrassing for this to happen to a boat of this quality," said Long Gone driver Bill Hodge after his engine experienced fuel-pump problems 500 yards past the starting line and cut off. Hodge got it restarted but ended up last in average speed of the nine GPI boats that ran yesterday in two heats.

Henry Knab, defending Gold Cup champion, was not able to even start a heat because of engine problems.

He and Hodge get another shot during today's two final qualifying heats to make the six-boat field for the Gold Cup and the $2,000 first-place prize money. Qualifying for finals in GPI and four other classes begins at noon. The GPI final will begin at 5 p.m.

Although the GPI racers are the heirs-apparent to the departed unlimited hydroplane class (thunderboats), most of the estimated crowd of 3,000 watching alon the East Potomac Park shoreline were turned by the slowest class, the Jersey Skiffs.

All the skiffs have the same size engine (243-cubic inch Chevy) and are identical in design. Standing still, they appear to be slightly reinforced rowboats.

Their only difference is how the mechanics adjust the cavitation plate on the underside of the hull: the angle of the plate determines how high the bow is above the water while the boat is in motion.

John Clark's Fast Buck stood the highest and pitched and bounced along the fastest (62.89) in the first heat. In the second heat, false starts by Clark and David Greenlaw in Veri Cheri forced both to cover an extra lap by penalty. Clark placed behind Mudflat Missle, which won in 56.71. CAPTION: Picture, Hustler, piloted by Bob Newman, holds lead on Long Gone in first heat of Grand Prix class. By James M. Thresher - The Washington Post.