In August, 11 master's degree students at Carnegie Mellon University accepted what seemed like a grunge assignment.

But when they delivered their results last week, people packed a Downtown meeting room to hear them.

"Believe it or not, all 11 of us have gotten really excited over vacant land management in Pittsburgh," public policy student Nathan Wildfire told a gathering of about 80 people, including Pittsburgh officials.

There's a lot to get excited about: Of 14,102 vacant parcels in city neighborhoods, possibly half contribute to blight. No one knows how many blighted lots there are because they have never been counted separately. The total vacant lot count includes parts of park land and all the privately owned, unlittered, kept-up vacant land on which there are no tax liens.

Blighted vacant lots, perennially distressing to neighborhoods and property values, have never been officially pitched as opportunity, even assets -- until recently.

At last month's first-ever Pittsburgh Green Forum, consultant Kate Dewey said, "Every once in a while, passion and opportunity come together. Maybe it's the Redd Up campaign, who knows? But right now, people are excited" about vacant land. "Everything is clicking."

Then, two weeks ago, the city reached agreement with Capital Asset Research Corp.'s parent company to buy back old liens -- tax debts -- on 11,000 properties. The city, Pittsburgh Public Schools and the Pittsburgh Water and Sewer Authority will pay $6.5 million to get back what was worth $64 million when they sold the debts in the mid- and late 1990s. The city will draw on a savings account to pay its portion.

During the years Capital owned the liens, the city's effort to return debt-ridden properties to the tax rolls was a torment. Besides the byzantine quest of finding absent owners, the city was up against wanting control of properties often worth less than their liens. And Capital obviously wanted its money.

With renewed control, the city will forgive or reduce the debts on the properties when it brings them to tax auction and be able to expedite neighborhood plans for the land.

In-fill housing has been the most common gap filler, but in-fill homes in blighted neighborhoods can be a hard sell, hard to keep occupied and even unnecessary. Other options are parklets, gardens and farms, which people in the neighborhood can run as community businesses, selling flowers and produce for income.

The report cites programs in Philadelphia, Baltimore, Cleveland, St. Louis and Chicago as having proven the wisdom of investment in green space. Based on such factors as property values and tax rates, the report claims that for every $1 of green investment the city makes, it can earn $2.09 after five years, not including the costs of stewardship. Philadelphia's nationally recognized lot reclamation efforts have yielded $1.57 per dollar.

The Carnegie Mellon report "Greening Vacant Lots for Pittsburgh's Sustainable Neighborhood Revitalization" calls specifically for the city to hire a Clean and Green coordinator in a nonpolitical position.

"Every successful national model we studied has a Clean and Green coordinator," Mr. Wildfire said.

The report recommends, too, that the city establish a pilot program in one neighborhood, greening "all vacant lots [in it] to prove the economic viability" of such a project, said Mr. Wildfire.

"It should be in a transitional neighborhood," he said, meaning one in progress but with its vacancy rate near the city mean, its green space limited and crime still above the city average.

The report alludes to many examples of vacant land turned into gardens and public spaces, and it cites two models in Pittsburgh as "best practice" efforts.

The Rosedale Block Cluster, a nonprofit community development group in Homewood, has bought 40 vacant lots since the late 1990s, and has been greening and maintaining them since.

It recently has expanded a horticulture program into its day-care center with PNC Grow Up Great money. About 600 youths have been trained in landscaping and business skills in the venture. A native plant production and nature center is being built on 10 contiguous lots between Brushton and Braddock avenues, said Diane Swan, executive director of the organization.

"We've just completed the heating and cooling system for our native plant production room," she said. "We claimed these lots. We've reduced litter and loitering. And all this evolved from a group clean-up day."

Steel City Bio-Fuels is seeking state and foundation grants to remediate contaminated soils by planting canola and mustard, which absorb and sequester contaminant heavy metals such as arsenic and lead in their roots and stalks, said Nathaniel Doyno, its executive director.

"We're proposing development of community-based businesses where we train people" to plant the seeds and handle the soil and then dispose of the plants once they have soaked up toxins, he said. "We plan to go to homeowners, doing soil tests and providing seeds and training" to help people get their soils clean.

"In the interim, you have tremendous visual impact," he said. "These plants are beautiful, bright yellow, and they bloom several times a year. They're hardy and don't require much maintenance."

The city Finance Department's real estate division already offers incentives for residents to buy or use vacant land. The "garden waiver" program lets a resident garden on a city-owned lot at no cost, but only as a steward; the city could sell it at any time.

The "side yard sale" option allows a resident to buy an adjacent city-owned property for about $200. The city has sold more than 450 side yards since starting the program in 1995.

The details of both programs are on the city's Web site, or are available by calling the real estate division.

Kim Graziani, Mayor Luke Ravenstahl's director of neighborhood initiatives, said the city has been discussing plans to hire a Clean and Green coordinator and initiate a pilot project.

"We are going to be rolling out a pilot project in several neighborhoods," she said. "I will lead it and start small and look at what the kinks are. We will be dealing with city-owned land to start with, and the goal is to have a planting by spring."

That deadline will require a launch only with land that tests clean.

"As we get further into it," she said, "we will look to partnerships" for such things as soil remediation.

She said the mayor wants the pilot program to partner with community stewards who can be relied on to follow through for the long haul.

"The only way this will succeed," she said, "is if people are committed to sustaining it."