Washington’s population is projected to expand to nearly 1 million residents over the next 30 years. (Andre Chung for The Washington Post)

The District’s population will continue to grow steadily and reach nearly 1 million residents in the next 30 years, according to a major new regional forecast, presenting some challenges for the city.

The city is projected to expand from 672,000 residents last year to 987,000 in 2045, when it will be just shy of replacing Prince George’s County as the region’s third-most-populous jurisdiction, according to the Metropolitan Washington Council of Governments (COG).

Fairfax and Montgomery counties will continue to rank first and second. They and other counties in the region will continue to grow. But only Charles County, which is a quarter of the District’s size, will gain population at a faster rate than the city.

The forecast, presented at a COG directors meeting Wednesday, is welcome news for the District. The city has taken pride in the steady recovery of its population since it hit a low of 565,000 in 1998 after decades of losing residents to the suburbs.

Mayor Muriel E. Bowser (D) and other officials like to boast about the number of cranes heralding new construction around the city. The District also relishes its reputation as a magnet for young adults of the millennial generation, who account for most of the city’s growth.

But the surge of arrivals also will test the city in important ways, especially in whether it can provide affordable housing and high-quality transportation.

“Our challenge is planning for growth while preserving the character that makes the District unique,” Bowser spokesman Michael Czin said. He noted that the mayor has committed to invest $100 million a year in a trust fund to expand and preserve affordable housing, as the city grows by nearly 1,000 residents a month.

Speaking of the housing pressures in the region, COG Chairman Roger Berliner said, “It’s important to understand that this is only going to intensify going forward.”

In a sign of concern about transportation, COG and the Greater Washington Board of Trade said they would host a high-level, regionwide forum on March 30 to discuss how to fix chronic problems with the Metro transit system.

COG has invited Bowser, and the governors of Virginia and Maryland to the invitation-only event, which it expects about 100 senior officials and business executives to attend.

The event is timed partly to mark the 40th anniversary of Metrorail’s opening. Hailed then as a model transit system, Metro has been plagued in recent years by safety lapses, unreliable service, troubled finances and falling ridership.

“We will begin a year-long investigation into what it would take to recapture Metro’s world-class status,” said Berliner (D), who also is a member of the Montgomery County Council.

Two long-standing problems to be addressed are finding a regionwide dedicated source of funding for Metro and streamlining its unwieldy governance structure.

COG Executive Director Chuck Bean, acknowledging the mixed emotions over the Metro anniversary, commented, “We’re not popping champagne. It’s more drinking a bottle of vegetable juice.”

COG considers this long-term forecast for population and jobs, called the “Cooperative Forecasts of Future Growth,” to be the most reliable projection available. It is the latest in a series of predictions conducted every five years that are based on both region-wide demographic and economic models, and on local jurisdictions’ own predictions.

A bright spot was the prediction that the region’s economic growth rate would recover to the point where it again exceeds the national average — despite the loss of jobs because of federal budget cuts known as sequestration.

The region began lagging the nation in economic growth in 2011 because of the federal spending slowdown, which has cost the region nearly $14 billion a year.

Nevertheless, from 2015 to 2025, the region’s job growth is projected to be 13 percent, compared with 10 percent for the nation.

The region will outperform the nation in job growth in the following two decades, as well, even though it is projected to lose 44,000 federal jobs by 2045.

The loss of federal government jobs will be offset mainly by a huge increase — more than 600,000 jobs — in professional and business services.

The forecasts were dismaying for Prince George’s County, but officials there said they thought COG was basing its predictions for the county on outdated data.

The county was projected to have jobs growth by 2045 of 19 percent, far below the forecast of 36 percent for the region.

Prince George’s also was predicted to have the slowest population growth — of 10 percent, to 991,000 residents — of any jurisdiction in the region.

David S. Iannucci, the top economic development adviser to County Executive Rushern L. Baker III, expressed doubts.

“I question the methodology that might have looked at 2013 or 2014 data for Prince George’s County and predicts what is going to happen in 2025,” Iannucci said.

He noted that 4,000 jobs are coming soon with the opening of the casino at National Harbor.

By contrast, the two counties projected to have the highest rate of job growth, by far, were Loudoun and Prince William. Each was expected to gain more than 100,000 jobs by 2045, which represented increases of more than 75 percent apiece.

Paul DesJardin, the COG official who oversaw the projections, said the growth in each county was expected to be concentrated around transit.

The region as a whole will add nearly 1.5 million people, to a total of 6.9 million, according to the forecasts.