“Columbia is going to make a whole lot of people in Harlem very happy,” a Harlem real estate broker, Willie Kathryn Suggs, said as she gestured out the window of a fifth-floor apartment for sale at 36 Convent Ave. Ignoring nearby City College, the ad for the apartment instead says it is “just north of the Columbia University Campus.”

The apartment’s views are impressive. The Hudson River shimmers to the west as Midtown Manhattan looms to the distant south. With 5 1/2 smallish rooms and one bath in 900 square feet, and a monthly maintenance fee of about $600, the asking price of $299,000 — the actual selling price will be lower — seems a good deal relative to, for example, the Upper West Side.

But the price is far higher than the apartment would have brought in 2003, when Columbia introduced a strategy to expand its Morningside Heights campus north into West Harlem — or Manhattanville, as Columbia prefers to call it.

If the new campus makes it over the many governmental and community regulatory hurdles, it will cover some 17 acres scattered between 125th and 133rd streets and Broadway and Twelfth Avenue.

“Columbia has big plans,” the apartment’s owner, James Lee, said. “There are going to be parks, a pedestrian mall, public entertainment, lots going on. The area’s going to be booming.”

In many ways, the hardworking Mr. Lee, a professional chauffeur, represents old Harlem — as does his building, which was taken over by the city in 1978, when its owner defaulted on the property taxes. Working with the tenants, the city’s housing agency set up a low-income co-op as a Housing Development Fund Corporation, a specialpurpose, tax-exempt, nonprofit entity authorized by the New York State Private Housing Finance Law. (New York has more than 1,000 HDFCs, housing more than 25,000 families.)

Income limits apply only to the initial purchase, after which a co-op owner’s income can increase to any amount. Income limits apply again on resale, though there are no restrictions — other than the market — on resale price.

The owners here paid $250 “a unit, and most don’t sell unless they’re leaving New York. But then they can turn their apartment around and get a lot of money,” Ms. Suggs said. Yet while owners can sell for whatever they can get, the price is naturally limited by the HDFC requirement that a buyer at 36 Convent Ave. make less than $144,000 annually.

The price may also be limited by the unhappiness of some co-op owners with high sales prices. On the day of an open house, two residents manned the front door to discourage would-be buyers. “We want to keep our building low-income and low-maintenance,” one said.

These days, it isn’t the market that’s impeding Harlem’s magnificent housing stock from receiving the capital investment it has long needed. Rather, it’s often the resistance of longtime residents, including owners of low-income co-ops like this one. “They’re caught in a time warp,” Ms. Suggs said. “They’re remembering the bad old days and think that they’re going to get pushed out. But they have no idea of what the real estate market is doing. There’s enough property in Harlem for everybody to live together peaceably.”

One Harlem brownstone owner, Lovelynn Gwinn, bought her house on West 138th Street, directly north of the proposed Manhattanville campus, in the relatively bad old days of 1998.

“It was brutal,” she recalled. “There was so much drug activity and prostitution going on.”

The block was so unkempt that it had far more rats than people. One day, the earth seemed to be moving in a nearby back yard because renovation had disturbed tens of thousands of nesting rats.

Today the block is serene and lovely. The block association puts its efforts into beautification rather than crime prevention. Small children play on the stoops where drug dealers once hawked their wares, and neighbors chat over their backyard fences.

Having paid $230,000 for her house under the city’s HomeWorks program, Ms. Gwinn considered putting it up for sale at the appraised price of $1.4 million.

“But that would be like selling short,” she said. “Columbia is bringing in people with money, and the neighborhood is getting retail and restaurants that look like downtown establishments. They don’t look anything like what had been here.”

Indeed, on Broadway people stream in and out of Ms. Gwinn’s favorite new places, Tres Pasos and Café Largo.

Even as Harlem becomes increasingly expensive, it remains a bargain compared with its neighbor to the south, the Upper West Side. Developer Hans Futterman said his “full-service condos” west of Frederick Douglass Boulevard will sell at 30% to 45% less than they would on the Upper West Side.

Mr. Futterman just sold two units in the gut-renovated townhouse on West 123rd Street where he lives — one for $1.2 million, the other for $1.1 million. “Each is a little over 2,000 square feet,” he said, “so that works out to about $600 per square foot.” Those same units, 40 blocks south, would sell for between $1,200 and 1,400 a square foot.

Meanwhile, the unhappiest Harlem residents may be the roughly 140 households that actually live within the proposed Columbia footprint — most in two city-owned buildings operated under the housing department’s Tenant Interim Lease program, which trains tenants to manage their buildings in anticipation of eventually owning them. “We don’t want to be moved out,” Luisa Henriquez, who lives at city-owned 602 W. 132nd St., said. “Columbia moving in is a bad thing because Columbia isn’t willing to share. They want everything.”

An adviser to Mayor Bloomberg and a professor of international and public affairs and political science at Columbia, Ester Fuchs, said: “The health of the city historically has always been about neighborhood transformation. For neighborhoods to stay the same is a recipe for a stagnant city.”