After July 1, if you catch a taxicab during the evening rush period in the District of Columbia and want to go into either Maryland or Virginia, or if you catch a cab at National or Dulles airports and want to cross the Potomac River, you'll have to pay -- for the first time -- a $1 surcharge.

The Washington Metropolitan Area Transit Commission, which controls interstate cab rates, announced the surcharge yesterday following a routine review. For the first time since 1982, it also approved modest increases in basic fares for all trips that cross state lines.

Under the new tariff, a trip for a lone passenger from National Airport to a point five miles distant in the District that now costs $5.70 outside the afternoon rush will cost $5.80. If two people are riding, a current $6.45 trip will cost $6.80. And that $6.80 trip, if made during the afternoon rush, will cost $7.80. That's in addition to National's 50-cent "gate fee," levied on each cab to pay dispatchers, making the total $8.30.

"It's the first time that the commission has dealt with a rush-hour surcharge," William H. McGilvery, its executive director, said. A surcharge has been imposed for several years for rides entirely within the District, but not regionally. Local governments regulate cab rates for trips made entirely within their own borders.

Here are the nuts and bolts, starting July 1: The basic charge of $1.70 for the first half mile will rise to $1.80. The subsequent distance rate, 50 cents for each half mile or fraction (basically $1 a mile) will be continued. The cost of each extra passenger will rise from 75 cents to $1. The rush-period surcharge of $1 per trip will be effective for each party that boards a cab between 4 and 6:30 p.m.