They have made it a priority at the United States Department of Transportation: Get people out of their cars.

This week, the department announced $848 million in grants to help cities discourage people from driving, in many cases by imposing new tolls or fees.

But at the same time, another arm of the federal government seems to be sending a very different message. Congress provides a tax break to many of those same drivers to help them shoulder the costs of taking their cars to work.

Close to 400,000 commuters nationwide - about half of them in the New York City area - take advantage of a provision in the federal tax code that allows them to use up to $215 a month in pre-tax wages to pay for their parking at work, according to executives at corporate benefits firms that specialize in administering the tax break.

While some drivers use it to pay for parking at commuter rail stations or bus stops, most take advantage of it to pay for parking near their workplace, mostly in city centers, the executives said.

The tax savings can equal about $1,000 a year for some drivers. And the effect makes driving to work more desirable.

"It is perverse," said Jeffrey M. Zupan, a senior fellow for transportation at the Regional Plan Association in New York. "If you're going to institute pricing measures that are intended to reduce the amount of driving, you don't want to keep in place other measures that encourage people to drive. What you want is a set of policies that work together."

MANY companies that have opted out of the tight Midtown Manhattan market in favor of Greenwich and Stamford office space are attracting growing numbers of young city dwellers who are turning the traditional commuting pattern on its head.

So-called "reverse commuters" - workers who live in New York City and commute to Fairfield County - are one of the more subtle indicators of the robustness of the Stamford and Greenwich office markets. The trend is particularly prominent in Stamford because the central business district has developed around the city's transportation center.

UBS, the giant investment banking and wealth management firm, which now claims more than one million square feet of office space in four Stamford locations, draws "several hundred" of its 4,500 workers from New York City, according to Kristopher Kagel, a company spokesman.

Jeffrey Zupan, senior fellow for transportation at Regional Plan Association, a nonprofit organization that monitors various planning issues across Connecticut, New Jersey and New York, said, "Reverse commuting works in Stamford because the city is developing in a way that can take advantage of it."

A significant increase in reverse commuters is reflected in ridership rates on the Metro-North Railroad. The number of peak-time riders in the morning who board at a New York City station and get off in Stamford has doubled in the last decade, and has increased nearly 150 percent since 1990, according to figures provided by the Metropolitan Transportation Authority.

New York-to-Greenwich ridership has increased at roughly the same rate, though the number of reverse commuters is smaller, with about an average of 870 commuters getting off there in the morning, compared with 1,900 in Stamford.