Overcharging passengers from National Airport can be hazardous to a cabdriver's economic health. A fourth hacker caught in a recent wave of enforcement had his District of Columbia permit suspended yesterday for one violation and faces even more serious discipline for 18 other alleged incidents.

Isaac Sowemino, who owns and drives a D.C. Checker cab, was given a 45-day suspension by the D.C. Hackers Review Board yesterday after he had charged lawyer Mark Davidson $9.95 for a ride that officials said should have cost $7.25 between the airport and an address in Washington's Kalorama neighborhood.

The formal accusation did not relate directly to the fare but rather to the driver's alleged misconduct. Davidson testified that Sowemino grabbed his suitcase and locked it in the trunk of his cab in an effort to enforce the excessive charge. Police were called and got Sowemino to release the suitcase.

Meanwhile, the Washington Metropolitan Area Transit Commission , which sets and enforces fares for cab trips that cross state lines, issued a formal order accusing Sowemino of 18 overcharges, including $33.80 for carrying one passenger from the airport to Bethesda that should have cost $15.50 and another for $13.10 for carrying a person to M Street in Washington that should have cost $6.35.

If found guilty, Sowemino could lose his right to serve National Airport, a sanction recently ordered against one other driver accused of systematic overcharges. One other lost his D.C. permit; another was suspended.

Gregory Paul Barth, transit commission general counsel, said Sowemino was called in last June after a series of overcharge complaints and was informally counseled on proper fares. Several months later, Barth said, complaints against him of overcharges resumed.