ILLEGAL PARKING is about to get more risky for thousands of scofflaws in the area-those who ignore parking rules and tickets because their cars are registered out of state. The District of Columbia, plagued by violations by suburbanites, is stepping up its use of two blunt enforces, the towtruck and the boot. In addition, a panel of the Metropolitan Washington Council of Governments is advancing a regional plan under which Maryland, Virginia and the District would refuse to renew the vehicle registrations of all those with a certain number of unpaid parking tickets anywhere in this area.

As District drivers know well, the city already uses registration as a lever for collecting parking fines in its own bailiwick. More than 60 Maryland localities have adopted a reciprocal pact. Cooperation across state lines has been slow to come, though, because suburban officials have not been inclined to help the District collect from their constituents. True, reciprocity would help the city most; Marylanders and Virginians owe about $6.3 million in unpaid District parking fines from 1976 alone. But the suburbs' losses, while much smaller, are mounting, too.

The COG proposal won a key endorsement the other day from the Prince George's County Council, which asked only that a new system be implemented region-wide, amply publicized-and not retroactively applied. That would be fine; the boot could still be used to collect old debts. The important thing is getting the suburbs and the two states' legislatures to agree that, in the future, all scofflaws will be fair game around the region.