In almost every neighborhood in Miami, from poorest to richest, from oldest to newest, from Hispanic to black, redevelopment is changing the traditional face of the city.

The widespread boom promises a metamorphosis in communities that have eluded progress for decades, and an improvement in Miami's global status as a destination for tourists and investors.

But with the massive development drive come challenges -- more traffic, gentrification that could drive poor families out of city neighborhoods, and skyrocketing property values.

In the last two months alone, several new ventures have emerged that are expected to pour up to $3 billion of mostly private dollars into areas that have been portrayed as the epitomes of blight: Midtown Miami in Wynwood; the Florida Marlins stadium in Little Havana; Crosswinds in Overtown; and the Miami Partnership in the Civic Center area.

While traditionally prosperous neighborhoods such as Brickell and the Upper East Side are also exploding with private development, it is the attraction of investors to these poorer communities that is most fascinating and worrying observers.

''When I got here six years ago, the words market and Overtown would never have been used in the same sentence,'' said Hodding Carter III, the president and chief executive officer of the John S. and James L. Knight Foundation, which has been involved in redevelopment efforts in Overtown.

Even some of the most neglected neighborhoods that have not yet attracted significant private development have received financial commitments from the government for major projects.

For example, the city is in the process of buying land to build a large park in Little Haiti with $25 million, and the Model City Trust is trying to give that area an overhaul by clearing several square blocks with public funding and inviting private developers to build new homes.

''I've never seen anything like this,'' said Miami historian Paul George, a professor at Miami Dade College. ``I've studied the booms of the mid-'20s, after World War II, and other smaller ones of the late '70s and early '80s, and none of those compare to this in terms of dollar value, the volume and scale of things being built, and the amount of places being impacted.''

Several factors have led to the boom: an unusually long period of low interest rates, political stability, a demand for housing.

Some of the credit -- or blame, depending on whom you ask -- must be given to Miami Mayor Manny Diaz. His bullish attitude on development and his eagerness to spread the wealth around to the poorer neighborhoods have become the hallmarks of his tenure.

A major theme in Diaz's election campaign in 2001 was to bring progress to all of the city's neighborhoods, and he hit that note again during his State of the City speech this year. He is proud of the results.

''This relentless attitude has permeated throughout the city,'' Diaz said. ``These opportunities don't come all the time. They come sporadically. You have to take advantage of it.''

Suddenly, it's not out of the question for developers to see the opportunities in vacant lots, abandoned structures and run-down rental buildings in Wynwood, Overtown, Little Havana, the West Grove.

Prime location is driving the demand. All of those neighborhoods are a five-minute drive from downtown.

The changes have not been embraced by everyone. Already, residents in red-hot development areas such as Little Havana and the Upper East Side have persuaded political leaders to approve temporary building moratoriums while planning issues are considered.

To them, development is a double-edged sword. They see more traffic, irrational zoning, tall buildings casting shadows over single-family homes. They see the working class being squeezed out of the city by a relentlessly rising real-estate market and higher taxes.

''They can't keep destroying our neighborhoods,'' said Josefina Sanchez-Pando, president of the Silver Bluff Homeowners Assocation, who recently formed an umbrella group of all the city's associations to lobby for ''responsible'' development.

``Development is going on at an insane pace. With all of these buildings, you need more police, more fire rescue, more hospitals, more schools, more infrastructure. And that has not been part of the plan. We have to keep all of this in mind. If development doesn't help, it destroys.''

Shane Graber, president of the Bayside Residents Association, which pushed for the moratorium along Biscayne Boulevard, said he is not opposed to development.

''We just want to make sure it's done the right way, with a balance,'' Graber said. ``Some of the projects that were pushed through are not within the spirit of what neighborhoods nor the city like for our area.''

Because of resident complaints, city commissioners approved the moratoriums to temporarily stop accepting new building applications from Northeast 36th Street to the city's northern limit along Biscayne Boulevard, and from Coral Way to U.S. 1 on Southwest 27th Avenue. The city wants to review its planning, zoning and building codes in the meantime.

Some activists believe that the city risks paralyzing itself with traffic if it doesn't address the transportation issue.

''Many of these projects, like the Midtown project, are really good,'' said architect Jorge Espinel, who teaches urban planning at Florida Atlantic University. ``But you can't do all these things without the proper large-scale transportation infrastructure. Neither the city nor the county are doing anything about it.''

Gentrification is also a concern. Many worry that the redevelopment could leave much of Miami unaffordable for the working class.

Already, Miami residents pay some of the highest rents in the country in proportion to their income.

In the city, 49 percent of residents who rent housing pay more than 30 percent of their income on rent -- generally considered too much by housing experts. Miami's rental rate is the highest among 23 cities studied by Living Cities and the Brookings Institution, based on 2000 Census figures.

It's not so much because rents are so expensive in Miami, but because wages are so low.

Rebecca Sohmer, a research analyst at the Washington-based Brookings Institution, said it is crucial for affordable housing to be part of the mix on development in poorer areas.

''If it's done right, you can have your cake and eat it, too,'' Sohmer said. ``You can have big development and help protect affordable housing.''

Carter, of the Knight Foundation, says it is also important that the development craze doesn't simply bulldoze over the historical character of neighborhoods such as Overtown, the traditional center of the black community.

The black population dropped by 15 percent in the city in the 1990s. And observers say it will likely continue to shrink.

Bruce Katz, another Brookings analyst, said the city should put some of the added tax revenue from the development boom into some sort of housing trust.

''Given the high level of poverty in Miami, this kind of market activity is positive,'' Katz said.

``The question is if the fiscal base grows, what are the higher revenues used for?''

IN THE MIX: Rarely used parking lots near Miami Arena would also become part of the $150 million mixed-use Crosswinds development. JOSHUA PREZANT/FOR THE HERALD

REVITALIZATION EFFORT: The Crosswinds project, which has not yet been approved, would create 1,000 housing units - more than have been built in Overtown in several decades. JOSHUA PREZANT/FOR THE HERALD

CIVIC CENTER AREA: Developers have purchased the old Mahi Shrine building and are trying to get permits to build a $300 million mixed-use development on the banks of the Miami River. TIM CHAPMAN/HERALD STAFF

OVERTOWN: A vacant building at 1001 NW Seventh Street would become part of the Crosswinds development. JOSHUA PREZANT/FOR THE HERALD

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