In the first such case in its 20-year history, Washington's regional taxicab regulatory agency has formally accused a taxicab driver of repeatedly overcharging riders he picked up at National Airport, and has ordered a hearing into the allegations.

In one of eight incidents cited, cabdriver Jack B. Dembo was accused by the Washington Metropolitan Area Transit Commission of charging two people $74.20 for what should have been a $21 trip from the airport to Bowie, Md. In another instance, he was accused of charging one rider $18.50 for a trip that should have cost $6.80 from the airport to the Shoreham Hotel.

The transit commission, which is responsible under an interstate compact for setting and enforcing cab fares for trips across state lines in the Washington area, leveled the charge against Dembo in the first formal order of its kind ever filed against an individual hacker. All previous taxicab violations have been settled by informal action, according to William H. McGilvery, the commission's executive director.

Two years ago, when cabdrivers demonstrated in front of the District Building seeking higher fares, Dembo -- an organizer of the demonstration -- mounted the hood of a parked taxi and advocated a strike and a blockage of traffic in an effort to obtain action. The next day, he was arrested at a D.C. Public Service Commission meeting dealing with cab fares and fined $10 on a charge of disorderly conduct.

More recently, he has served as a volunteer member of the mayor's task force on taxicab industry problems.

Dembo could not be reached for comment on the transit commission's unprecendented issuance of a formal order citing him for the alleged overcharges of passengers picked up at National on eight occasions between May 4, 1979, and Feb. 13, 1981. On all occasions, McGilvery said the passengers involved filed written complaints.

In addition, the commission's order said Dembo refused on one occasion to comply with a fare's request for a receipt, and on another occasion issued a receipt giving a false identification.

The commission itself has no specific disciplinary authority. In its order, it said it would hold a hearing April 21. If it finds the allegations valid, the order asserted, the commission could recommend possible administrative action by the District of Columbia to suspend or revoke Dembo's hacker's permit, and noted specifically that it could refer the matter to the District Corporation Counsel for possible criminal action if it found that action was merited.

Under the region's fragmented cab-regulatory system, the Federal Aviation Administration regulates cabloading operations at National Airport, which is in Virginia; the transit commission sets the fares across the Potomac River into the District, and the District has the power to discipline D.C.-licensed cabbies, such as Dembo, for violations of the rules.

In the most recent incident disclosed publicly, a D.C. government official last week announced a two-week suspension of another driver accused of improperly refusing to drive a member of Congress directly to her destination on Capitol Hill until after she protested.