A resurgence of population growth in the Washington metropolitan area, fueled primarily by development in the Virginia suburbs, is transforming the region into the hub of a "mega-metropolis" that contains 7.8 million people and extends from Baltimore to Norfolk, according to a population report to be released today.

But the report, prepared by the Greater Washington Research Center, warned that the continued rapid development of Fairfax, Montgomery and Prince George's counties is running ahead of efforts by their governments to provide roads, sewers and other public services.

"We've got some real serious problems which the local jurisdictions better address," said R. Robert Linowes, a Washington lawyer who is chairman of the research center.

"You have never seen new capital improvements until they are at the critical stage," he said. "Roads and improvements don't get built until everybody is choking. Until pressure is applied to make local officials act, they don't act."

Linowes, who handles planning and zoning cases, characterized the center's findings as a "good news/bad news report." He said there was reason to be optimistic about the movement of people back into the District and its suburbs.

More serious, he said, has been the failure of officials in many jurisdictions to provide adequate funding for the public improvements needed to handle the region's growth -- a finding that drew criticism from some officials.

"I don't think they know what they're doing," said Fairfax County Board Chairman John F. Herrity. "I don't have to spend 10 cents to tell you there's a traffic problem in Fairfax County, but I think we're making strides in addressing the problem."

Linowes leveled his harshest criticism at officials in Montgomery County, where he lives, declaring: "They just are not doing anything at this time to address this issue."

"That's totally inaccurate," retorted Lewis T. Roberts, Montgomery's chief executive officer. Roberts said the county spent $40 million last year on road improvements and adopted a $188 million capital improvements program for the next six years.

"In growing, urbanized areas there will always be some degree of congestion, no matter what the jurisdiction does," Roberts said. "We would put our performance and the amount of money we are allocating on road improvements up against any other jurisdiction in the Washington area."

There was no dispute, however, over the report's central finding that people are moving into the Washington region at a rate that is well ahead of the growth rates of major metropolitan areas in the East, trailing only the Sun Belt and West Coast cities of Houston, Dallas and Los Angeles.

The report said metropolitan Washington's population increased by 158,000, or at a rate of 5.2 percent a year, from 1980 to 1984, eclipsing the small increase registered during the previous decade when the area's growth "ground virtually to a halt."

The research center, a nonprofit organization that monitors demographic trends, said that, in contrast to the suburban growth that was dominant in the 1970s, the District and its immediate suburbs have become the most sought-after places in the region.

Rapid growth in the outer suburban areas appears to have been slowed, the research report said.

"Since 1980, traditional growth patterns in the greater Washington region have literally been turned inside out," the report stated.

"The former pattern of population increases, mainly on the outskirts, with stagnation or loss in the center, has shifted to accelerating growth close to the center and decelerating increases along most of the outskirts," the report said.

Among the report's findings:

*The population explosion continued in the "big three" suburbs of Fairfax, Montgomery and Prince George's counties.

Fairfax has registered annual net gains of more than 18,000 people since 1980, while Montgomery has grown by an average of 10,600 each year and Prince George's by 2,500.

*The more distant suburban areas of Loudoun, Charles, Frederick, Howard, Calvert and Anne Arundel counties saw what had been a rapid growth rate during the 1970s cut in half during the first five years of this decade.

The exception was Prince William County, which has maintained a moderate growth rate.

*After experiencing a population loss of 118,000 during the 1970s, the District has lost only 11,800 people during the first half of this decade. Its population has leveled off at about 623,000.

*Alexandria and Arlington registered small population increases between 1980 and 1984, reversing losses during the previous decade that saw Alexandria's population fall by nearly 800 a year and Arlington's by 2,200.

*Taken together, the overall growth of the Washington region presages the emergence of a 250-mile-long megalopolis that could rival the Chicago area, now the third largest combined metropolis in the nation, in the number of residents and buying power it contains.

"This evolving economic colossus extends all the way from the Pennsylvania border on the north to the North Carolina boundary on the south, and from the Chesapeake Bay on the east to the Appalachian Mountains on the west," the study said.

Research center officials said the extension of the Washington region deep into Virginia can be explained by the fact that the Washington metropolitan area "already adjoins metropolitan Baltimore" and is separated by "only a single county, Spotsylvania, from the Richmond-Petersburg metropolitan area."

That region, the study said, adjoins the Norfolk-Virginia Beach-Newport News metropolitan area.

George Grier, the consultant who prepared the report, said its message is that the District is becoming increasingly attractive to people who previously opted for suburban life.

Contributing to the city's resurgence, Grier said, is its appeal for urban-oriented singles and young couples, and a growing dissatisfaction with massive traffic congestion in the suburbs.

"People are getting tired of making those commutes," he said. "They have run into a lot of expenses and a lot of extra time, and they don't like it."

Grier and Linowes cited several implications of the changing demographics, including the need for a reassessment of decisions based on earlier population trends that resulted in the closing of many schools and the failure to appropriate funds for roads and other public improvements.

Herrity said the research center was off base in questioning Fairfax's efforts. Including the $135 million road bond issue passed this year, the county will be spending nearly $250 million on road improvements during the next four to five years, he said.

Linowes acknowledged Fairfax's road program, but contended that it is not enough.

Fairfax officials have questioned the Greater Washington Research Center's reliability ever since it issued a report in 1982 that predicted that local governments would be hit by large deficits by the middle of the decade, he said. That projection has proven to be wrong, Herrity said.

"As far as we're concerned," he said, "they have limited credibility."

But Thomas Downs, the District's city administrator, said that the center's findings are consistent with the District's projections that its population is stabilizing and will increase gradually during the next several years.

"I am much more comfortable with moderate growth projections, because it allows time to absorb people into the city" and plan for necessary public services, Downs said.

"Explosive growth," he added, "can be just as detrimental as large declines."