Say the words "commuter tax" and almost everyone in the Washington area shudders, either in delight or disgust. In the District, a commuter tax is the pot of gold at the end of the political rainbow. In Virginia and Maryland, it's pure poison, as popular as a rush-hour traffic jam.

But ask a few questions and it becomes clear that almost no one knows exactly what a commuter tax is, how it would work or who ultimately would get stuck with the bill.

This is the season when talk about a commuter tax traditionally flourishes. As the District prepares to elect a mayor and council, candidates are looking for ways to finance the government without raising voters' taxes. D.C. Del. Walter E. Fauntroy (D) recently became the first of this year's mayoral contenders to suggest putting the bite on Maryland and Virginia residents by seeking to impose a tax on commuters' incomes.

Most politicians in the District and both states agree a commuter tax will not materialize anytime soon, if ever. The District is legally barred from taxing commuters; members of Congress from Maryland and Virginia inserted a clause banning such a tax in the charter granting self-government powers to the District. Lawmakers from those states have no apparent incentive to change that position.

But in many other metropolitan areas -- Philadelphia and New York, for example -- commuter taxes have long been a part of life. The way the taxes are levied varies widely, as does their financial impact on the people who pay them.

Should proponents of a commuter tax succeed in bringing the idea to Washington, it would have two primary effects. One is obvious: it would provide a financial windfall for the District government. Officials estimate that if commuters' incomes were taxed at the same rate as those of D.C. residents, city government would get an additional $1 billion.

But the other effect is surprising: The commuters who pay the tax might feel only a limited financial pinch, while the potential impact on state governments in Virginia and Maryland is significant.

According to officials in both states, commuters would be allowed to deduct any tax they pay to the District in the jurisdictions where they live. Again, if commuters' incomes were taxed at the same rate as D.C. residents', Maryland and Virginia residents' tax bills would increase somewhat, because the District's income tax rates are higher than those of the two states.

Under these conditions, deductions would wipe out all the income tax money both states collect in the Washington suburbs. Such a loss would wreak havoc on budget-makers in Annapolis and Richmond.

Even if the District taxed commuters at a lower rate than residents, a standard that is common in other areas, the loss of revenue could create major money troubles for the states. Virginia and Maryland would be forced to look for new sources of revenue or possibly to alter their tax laws, shifting the commuter tax burden directly onto those who pay it.

"There would be a direct, dollar-for-dollar reduction in revenue to the state of Maryland for any {commuter} tax collected in the District," said Ken Mannella, a tax specialist in the state of Maryland's Washington office. "That money would come directly out of the state treasury . . . . You have to ask what would happen politically if there were this kind of revenue hemorrhage."

Virginia Tax Commissioner William Forst said that more than a third of his state's income tax collections come from Northern Virginia, and that a commuter tax would cost the state "a very significant amount." Under current law, Forst said, "Every resident of Virginia who works in the District wouldn't pay Virginia income tax any more."

In many parts of the country, commuter taxes have been a fact of life for decades. Most of the taxes are income taxes applied to the paychecks of people who work jobs in central cities but live in the suburbs.

According to a recent study by the Advisory Commission on Intergovernmental Relations, most cities that have commuter taxes levy a flat-rate charge that is somewhat lower than the tax charged to city residents.

New York City, for example, levies a tax of 0.25 percent on commuter incomes; residents pay income tax at rates ranging from 1.5 percent to 3.5 percent. One of the highest income taxes is in Philadelphia, where commuters pay 4.315 percent and residents pay 4.96 percent. San Francisco and Los Angeles do not directly tax commuters, but charge employers a payroll tax of 1.5 percent and 0.75 percent respectively.

Virginia and Maryland lawmakers who oppose a commuter tax argue that it is inherently unfair because it forces nonresidents to support a government whose leaders they have no part in electing. That, they say, would be taxation without representation.

They also argue that commuters contribute significantly to the District's treasury through taxes on restaurant meals and retail purchases made in the city.

Proponents, however, say nonresident taxes help pay for essential city services that commuters use, such as streets and utilities. And in parts of the country where Congress has not specifically outlawed commuter taxes, courts have agreed with this argument. Since the early 1960s, major court decisions have upheld the legality of many commuter taxes.

In the Washington area, the District government is the only agency that has closely studied the potential financial impact of a commuter tax. As part of the 1991 budget, officials projected what would happen if Virginia and Maryland commuters were taxed at the same rate as D.C. residents.

Under current law, District residents pay a top income tax rate of 9.5 percent on all income over $20,000. Maryland residents pay a combined state and county income tax rate of 7.5 percent on all income over $3,000. Virginia residents pay a top tax rate of 5.75 percent on all income over $17,000.

The District government would gain almost $1.2 billion in revenue, while the state of Virginia would lose more than $593 million and the state of Maryland would lose more than $650 million.

Suburban lawmakers such as Rep. Stan Parris (R-Va.) say that such revenue losses "would be disastrous" for their states. Parris calls a commuter tax "faulty public policy and an irresponsible evasion of the {District's} obligation to get its fiscal house in order."

But District officials such as Deputy Mayor for Finance Robert Pohlman say a commuter tax would shift part of the burden of paying for city services to people who currently use them but do not pay. "The District is in a double bind" because commuters cannot be taxed and because the federal government has not increased its payment to the District for several years, Pohlman said. "Equity would call for a solution involving one or both of these areas."