The District could add 250,000 residents over the next two decades under a new vision for the city that Mayor Vincent C. Gray will unveil Tuesday, which includes vast long-term changes for how residents travel, eat and enjoy the outdoors.

In 20 years, nearly everyone would get around by foot, bicycle, new streetcar lines, bus or Metro. Homes and apartment buildings would feature compost piles and adhere to more aggressive recycling standards. Roofs would be green, and the city government would monitor fossil fuel consumption.

When residents want to eat, they wouldn’t have to walk more than a few blocks to find fresh fruits and vegetables. And if they want to catch their own food, residents would be able to wade into the Potomac and Anacostia rivers, throw out a line, and reel in a striped bass or white perch because waterways would be “swimmable and fishable.”

“We are deadly serious about this,” said Harriet Tregoning, the city’s planning director. “We have all these people who are moving to Washington. . . . We can take this opportunity and redefine our city in some important ways.”

After a six-month review that included 125 meetings and more than 700 community participants, Gray (D) has finalized what he calls a “Vision for a Sustainable D.C.” by 2032.

The plan includes short-, mid- and long-term policy goals that Gray hopes will guide his and future administrations. However, the proposal does not include funding sources for goals that could cost billions of dollars to implement, making some of them dependent on aid from an already cash-strapped federal government.

“It’s a statement of where the mayor thinks the city’s values and direction should go,” said Robert H. Nelson, a professor of environmental policy at the University of Maryland. “But whenever anything comes up that is actually going to cost money, this statement is not likely to have a huge impact in terms of the debate. . . . Anything that has a 20-year goal becomes more symbolic.”

Although some ideas seem improbable — such as being waste-free within 20 years — administration officials said the plan would help local officials conceptualize the future of the city. Some changes could begin immediately.

“They may seem far-fetched given our history as a city, but not so much if you look at what other cities around the world are doing,” said Christophe Tulou, head of the D.C. Department of the Environment. “The goal is to have D.C. be visionary in as many areas as possible and, when you add it all up, for D.C. to be the greenest, healthiest, most livable city in the U.S.”

According to the report, a copy of which was obtained by The Washington Post, the administration is hoping to require “energy audits” of all buildings “periodically and at the point of sale” within a few years to gauge their usage. Also in the short term, online tools or forums would allow residents to calculate energy usage.

The short-term efforts to highlight energy use would set the stage for potential long-term strategies for pricing fossil-fuel reliance. The plan calls for a 50 percent reduction in emissions and energy consumption in 20 years, and envisions a 500 percent increase in green jobs.

In the area of transportation, the plan calls for 80 miles of bicycle lanes within a few years, about one-fourth more than exist today.

In another short-term goal, the city plans to reexamine its parking rules to continue to urge residents to use mass transit while ensuring an adequate supply of on-street parking. By 2032, after the city’s proposed 37-mile streetcar network is completed, officials are optimistic that 75 percent of all trips will take place on foot, bicycle or on public transportation, according to the report.

Changes in transportation would be needed because planners envision a dramatic increase in the city’s population.

Tregoning said the goal of adding 250,000 new residents is designed to build on what has “been a solid decade of population growth.” Last year, the Census Bureau found the District was the fastest-growing “state” in the nation after its population grew by 2.7­ percent in a little more than a year, boosting the city’s population to nearly 618,000.

Gray’s sustainability report envisions those growth rates continuing for another two decades, but demographers are skeptical.

“I think it’s likely to grow a bit more. Whether it’s sustainable over the next 20 years is hard to say,” said Peter Tatian, a senior research associate in the Urban Institute, adding that potential federal budget cuts and a lack of affordable housing could quickly dampen growth expectations.

Regardless, Gray’s plan envisions a far different city in the coming decades.

The plan calls for boosting the city’s tree canopy from 35 percent to about 40 percent, requiring the planting of thousands of trees. Eventually, a “three-track” trash-collection process including composting would be created to try to achieve 100 percent waste diversion.

The city’s waste-diversion rate is 23 percent, compared to San Francisco’s 70 percent, officials said.

To slash obesity rates in half by 2032, the city would place a renewed focus on enticing residents into physical activity and redouble efforts to combat lead poisoning.

Conceivably, in the long-term, city officials hope that activity could entail more recreation on the cleaned-up Potomac and Anacostia rivers.

One of the plan’s most ambitious planks calls for those rivers and Rock Creek to be “swimmable and fishable” by 2032.

Tulou said the District and Maryland are making great strides toward that goal, including stringent new stormwater run-off standards in the city and a recently launched $2.6 billion project to build two new tunnels to prevent sewage from spilling into local waterways. Last year, Baltimore officials announced an initiative to make the Inner Harbor swimmable and fishable by 2020.

“All of the pieces of the process are falling into place,” Tulou said. “It’s not an easy lift in terms of commitments and investments, but we are well underway. . . . If it hasn’t rained in a while, you can safely swim in the Anacostia and Potomac already.”