An expected 100 limited hydroplane racing boats - but none in the unlimited class - will compete in the President's Cup Regatts on the Potomac River near Hains Point today and tomorrow, beginning at noon.

The cup competition will feature racing teams with 7-litre, 5-litre, 225-cubic inch and 280-cubic inch hydroplanes vying for the solid gold trophy valued at more than $100,000 and originally chartered by President Calvin Coolidge in 1926.

This year's format will be different from past years since the unlimited boats will not be competing, according to Bennet R. Miller, regatta association president.

It was incorrectly reported in yesterday's edition of the Weekend section that the unlimiteds would be racing.

"Since one of the objectives of the President's Cup Regatta, as a non-profit organization, is to raise money for charitable contributions," Miller said, "we could not justify a guarantee of large sums of money without raising admittance fees to a point that would be out of range of the boat race fans."

Regatta spokesman Charles Garnett said the unlimited hydroplane association wanted an appearance guarantee of $1,5000 per boat. Anywhere from seven to 30 boats might have shown up, Garnett said.

There also were requests for as much as $25,000 to $40,000 in prize money, he said. In past years, the Regatta has paid as much as $1,000 inappearance money per boat and $20,000 in prize money, Garnett said.

Other meets in the unlimited hydroplane racing circuit have appearance and prize money. But Garnett said, since the President's Cup Regatta is sponsored jointly with the National park Service, on federal territory, commercial sponsors are not permitted.

The regatta is staffed by volunteer organizations, such as the Lions Club and Boys Clubs, which get a percentage of the gate for their charitable concerns, Garnett said.

Since the racing layout of most hydroplane courses is a tight oval, the lap, heat and average speeds of the invited classes of hydroplanes often equals or surpasses those of the unlimiteds, he said.

There will be 12 qualifying heats each day, running from noon to about 5 p.m. The preliminary heats will include Super Stock boats and Jersey Speed Skiffs, together with the four hydroplane classes.

There will be spectator viewing areas on both the Hains Point area in Washington and the Virginia shore-line below the 14th Street Bridge and National Airport. Admission to the Hains Point are is $4 for adults and $1 for children under 12. On the Virginia side, admission is $4 for the car and driver, $3 for adults and $1 for children under 12.