Marty Niles conquered handling problems to drive Mist America III to a narrow victory in the second heat of the seven-liter division and capped a perfect day for the Winter Haven, Fla., crew at the 47th annual President's Cup Regatta yesterday at Hains Point.

Nile's stretch-run triumph added some excitement to an otherwise lack luster first day for the regatta, which produced only eight heats with 13 boats and was watched by a crowd of only 5,000, according to National Park Police estimates.

The lack of enthusiasm among participants and spectators was apparently because of the absence of the unlimited hydroplanes, which are not racing in the regatta for the first time since 1969 because of a dispute over prize money.

"The facilities are good, but D.C. waited too long," said Niles, who added that he heard of the competition only a week ago. "Right now, there's a regatta in New York, a race in Canada, a race in Delaware. They waited too long to let people plan. We have our whole summer planned. The only reason we came here is we have an open weekend."

Niles averaged 85.066 miles per hour to win the first seven-liter heat over the three-lap, 1 2/3 mile course, holding off Big Bwana, driven by Henry Knab of Oceanside, N.Y., at an average speed of 84.906 mph. But somewhere between the end of the first race and the beginning of the second, Mist America 111 lost its cavitation plate, which sits over the propeller and keeps the boat glued to the water. The propeller also was dented, but despite trailing Bo's Ghost, the only other entrant in the second heat through each turn, Niles was able to catch up in the straightaways.

If Niles and his crew can replace the plate and propeller, Mist America 111 should be the favorite to capture the treasured President's Cup today when the seven-liter boats replace their stock engines with racing engines.

The super sport division produced the next most competitive heat of the day as Intimidation, handled by Rick Berthold of Fox River, Grove, III., narrowly held off Yellow Side Up, maneuvered by Baltimore's Michael Smith, with a winning average speed of 73,892 mph. Earlier, Intimidation averaged 75 mph to easily outdistance Bad News, with Daniel Ziegfield of Cockeyesville, Md., at the controls. Yellow Side Up was a close third.

Rubber Ducky, with Springfield's James E. Coan at the wheel, easily won both heats for boats with 280-cubic-inch engines. Veri-Cheri, driven by David Greenlaw of Yardley, Pa., was first in both heats for Jersey speed skiffs.

First-place finishers won $400, second place earned $100, and third place $50.