Most construction projects don't attract spectators. Not many people like to spend their free hours watching the slow movement of bulldozers, cranes, earthmovers, and cement mixers working on a building that is years away from completion. But that's not true at River Avenue and 162nd Street in the Bronx, where spectators dawdle to observe the work in progress morning, noon, and night.

It's not every day that New York City gets a new ballpark, and the diamond emerging from this empty lot won't be just any sports arena. It will be the new Yankee Stadium, replacing its next-door neighbor, a sports shrine built in 1923 that has been the showcase for the unforgettable exploits of men named Ruth, Gehrig, DiMaggio, Mantle, Jackson, and Jeter.

It is hard to overestimate what the new construction means for the Bronx, a down-and-out borough for decades but which has in recent years showed marked signs of resurgence. The decision of Yankees owner George Steinbrenner to stay in the Bronx rather than move to a newer, greener pasture in Manhattan or New Jersey means the Bronx Bombers will stay put for another half century or more. City officials and local residents believe the gargantuan investment - estimated at $1.2 billion - will spur housing redevelopments and the creation of jobs and retail businesses.

"Ten years from now, it's going to be beautiful here," says Lon Wilson, a lifelong resident and racewalking coach who likes to spend some of his free time watching the construction teams and taking pictures of the progress. "They say in the plans that we're going to get a new stadium, a 10-story hotel, new stores, a Target, a new train station. We're going to have concerts again in the neighborhood, like in the old days when I saw James Brown and the Isley Brothers at the stadium. The whole area will be rejuvenated. I'm a homeowner; I should reap the benefits. If the Yankees were to leave, the whole area would depreciate."

This scene is being repeated across town, where the New York Mets are building a newer, better ballpark to replace Shea Stadium, a generally unloved park that opened in 1964 next to the New York World's Fair in Flushing Meadows, Queens. The new stadium - now called Citi Field - is being more closely integrated into the cityscape than was Shea, which is isolated from city streets and surrounded by acres of parking lots.

It has been almost 50 years since New York City got a new major-league ballpark, and during that time, it lost both Ebbets Field and the Polo Grounds. Now it is getting two brand-new stadiums, both set to open in 2009 as potent symbols of the city's impressive recovery from the economic shocks that began in 2001. The huge construction projects, funded largely by the teams, not the public coffers, offer city planners a rare opportunity to use private investment to improve needy neighborhoods in the Bronx and in Queens, boroughs that are often out of the limelight because of the intense focus on Manhattan.