Some 30 Elm City residents and officials met in the Edgewood School Library Wednesday night for Mayor John DeStefano Jr.’s third go-around at making a case for long-term economic development in downtown New Haven.

Elaborating on themes from two previous meetings this year, DeStefano talked primarily about what he called the need for a concentrated expansion in the city’s commercial district. The mayor focused on his proposed “urban infill strategy” to increase the density of the downtown area over the next 10 years.

In a question-and-answer session at the end, residents mostly raised questions about the logistics of the plan, although one audience member asked how the plan might factor into the city’s current mortgage crisis.

“The downtown is a very small area, but it is a very rich area to grow jobs and revenue,” DeStefano said near the beginning of the meeting.

DeStefano’s “urban infill strategy” would require utilizing vacant land, dividing large blocks and narrowing streets in order to create a densely packed commercial district in under-utilized and abandoned areas, he said.

The mayor said he thinks such redevelopment will be key to creating the 22,299 jobs and employing businesses he anticipates.

The five areas in which DeStefano’s plan would call for expansion over the next 10 years are Gateway Community College, Route 34 East, Route 34 West, the Medical School and Long Wharf Road.

As the largest source of tax revenue in New Haven and an essential player in the downtown area, Yale would play a central role in the mayor’s expansion efforts, he said.

The proposed addition of two new residential colleges — which DeStefano said he has supported since the University officials approached him with the idea years ago — would have both positive and negative impacts on the city, he said. In the past, Yale’s growth has generated more jobs, but sometimes at the cost of valuable property that could potentially be used for commercial purposes, he said, though the two new colleges would not be located downtown.

“The only problem with sleeping with a friendly 800-pound gorilla is sometimes it rolls over in its sleep,” DeStefano said, citing Leonard Smart, the associate director of the Greater New Haven Business and Professional Association.

When asked by one resident how the city would attract retail businesses downtown, DeStefano cited the Medical School as an example of one area ideally suited for retail expansion. A density of residential and institutional development can draw retail business of its own accord, he said.

“The hospital is a dramatically under-used asset,” DeStefano told the audience.

He said the Medical School should pursue the same sort of commercial growth that Yale and the city have pursued around central campus. DeStefano contrasted the restaurants around Chapel Street with the food carts near the Medical School — the only places, he said, where people in the area can grab lunch.

But, he said, the city has yet to reach out to the Medical School to discuss mutually beneficial commercial expansion in the neighborhood.

“The city never said directly to the Medical School that they should expand — that it would be good for them and good for us,” DeStefano said.

As part of this expansion, the mayor wants to convert Route 34 from a highway into an “urban boulevard” in order to reconnect the Medical School with Yale’s central campus, he said.

But meeting attendees questioned where the money for such a conversion would come from.

“If there is any possibility of converting Route 34 into an urban boulevard, to what extent can federal dollars help to pay for such a conversion?” one resident asked the mayor during the question-and-answer session.

DeStefano responded that since the state on its own would not be able to afford the project, construction would require federal funding.

In response to a question about how the mayor’s plant might affect the city’s current rate of home ownership, DeStefano insisted that there simply is not enough land in the city to raise home ownership right now.

Looming in the background during Wednesday’s conversation was the national sub-prime mortgage crisis, to which New Haven has fallen victim. DeStefano told the attendees that foreclosures were up 40 percent between 2006 and 2007 and that out of 55,000 housing units in the city, 75 percent are rented, not owned.

Because the problem affects residential areas more than the commercial district, DeStefano said, it should not have a major impact on the redevelopment of downtown.

The last of the four meetings will be held March 18 at the Martinez School Library at 100 James Street.