IN MANY WELCOME WAYS, the lines that divide this city and its surburbs have been blurring, giving way to more interjurisdictional cooperation. But one surefire way to sharpen the dividing lines is to bring up the idea of the city's levying any tax on the incomes of suburban residents who work in town. If you live in Maryland or Virginia, it's referred to as the "commuter tax" - for that's become the imflammatory description. People in the city prefer the more technically accurate label, "reciprocal tax," since the tax also could be imposed by Maryland and Virginia on incomes earned in these states by residents of the District.

For the most obvious political reasons, every elected official from those states will blast the idea with both barrels every time it's discussed. These days - though maybe not in the future, as work patterns change - such a "reciprocal tax" would work to the District's financial benefit and the suburds' loss. In effect, it would constitute a raid on state and local treasuries. And these losses would have to be made up by other taxes. Moreover, the people in Maryland and Virginia have a financial stake in their health care, school, public safety and similar local services that they don't wish to forfeit through any formula under which they'd pay income taxes to the city instead of to their states.

As a result of this unanimous opposition from the two states, Congress stuck a provision in the city's charter act that specifically prohibits the city council from imposing any taxes on the personal income of nonresidents. And last week, the old war of words erupted again at House subcommittee hearings on various measures to lift the prohibition.

The section should be repealed. Quite aside from either the political or ultimate financial wisdom of imposing such a tax, this city ought to be able to exercise this right in the same manner as any other locality in the nation. That was what Mayor Washington told the House subcommittee in forceful testimony. Recalling the insertion of the tax restriction in the so-called home rule charter act, the mayor commented, "You can't say, 'you're free, now put your hands behind your back so we can tied tie them.'" Rather, said the mayor with a smile, he wants both hands free "to reach out and touch Virginia and Maryland."

To listen to the suburban officials, however, you'd think this kind of tax was unheard of - when in reality, both Virginia and Maryland do tax nonresident workers from several other states. Indeed, there are similiar taxes in more than half the states in the nation. And the House subcommittee chairman, Rep. Ronald V. Dellums (D-Calif.), who has introduced a repeal bill for the city notes that "We have an obligation to remove ourselves as colonists for the District of Columbia." Another supporter of legislation allowing the city to impose such a tax is Rep. Stewart B. McKinney (R-Conn.), who notes that he has many constituents who pay a tax to New York City because they work there.

There is a serious question as to how fast or furiously the city should move to impose the taz, since any unilateral action could result in costly retaliation by the suburbs. But that's a long way off; for now, Congress should act to eliminate the discriminatory restriction in the city's charter.