An influx of young professionals into new housing near Arlington Metro subway stations is expected to increase the number of county residents 14 percent during the 1980s and reverse a decade of declining population, according to county planning officials.

About three-quarters of the growth is projected near Metro stops from Rosslyn to Ballston and from Pentagon City to National Airport. Arlington's population, which declined 12 percent from 1970 to 1980, is expected to rise from 152,599 in 1980 to 173,799 in 1990, according to county median estimates. The population is projected to reach 191,155 in the year 2000.

"The increase in population hopefully will be enough of a contributor to the tax base to enable current residents to live without any large increase in their taxes," said Walter L. Frankland, a Republican County Board member who has long advocated tax cuts.

"I think the population trend is healthy," said board member John G. Milliken, a Democrat. "It's important for the community."

The projections, which Terry Russell, a county planner, said are educated guesses, reflect the expected impact of the County Board's recent rezoning of land near several Metro stops for more intensive commercial and condominium development. The zoning changes are expected to attract affluent single people and small families who demand little in costly public services such as education and public assistance while paying taxes on premium real estate. These residents are then expected to spur continued commercial growth near Metro stations, thus boosting tax revenues even more.

The projections assume the slumping housing market will recover and that household size will decline slightly after a decade of sharp decrease as children left home and smaller one- and two-person households replaced larger ones.

On the other hand, Alexandria -- an city inside the Beltway with four present or planned Metro stops compared to Arlington's 10 -- also is expected to reverse a decade of population decline but grow only from 103,217 in 1980 to 104,217 in 1990, according to city median estimates. Alexandria planners expect the city population to remain about steady until the year 2000 and they expect continued declines in average household size, which they say will largely cancel out any increase in residents.

Projections by the Tayloe Murphy Institute at the University of Virginia show a small increase in the number of Arlington residents from 152,599 in April 1980 to 153,400 in July 1981. Though institute associate Michael A. Spar said the increase is too small to be statistically accurate, it is the first one indicated since 1971.

"They're probably correct in saying the decline in average household size is going to taper off," Spar said of Arlington's projections.

The household size will level off in Arlington because it is already so low--about two persons--said John C. McClain, assistant director for planning and forecasting for the Metropolitan Council of Governments.

But Spar, McClain and Russell said that Arlington's predictions are dependent on interest rates and the resurgence of construction and home buying.

"Assuming we go back to . . . a normal residential market, I'd feel fairly confident that we'd achieve that kind of population growth," said Gary Kirkbride, Arlington planning supervisor. "The thing that's really unknown . . . is when the real estate market is going to come back."

"A lot of the population has come into the county because of the influx of new business into Rosslyn and Crystal City," said Arlington Board Chairman Stephen H. Detwiler. "These people enjoy the convenience of being close to work." With the projected population increase, the number of people working in Arlington also is expected to increase 23 percent in the '80s, according to median estimates by county planners.

One example where Metro development sparks new residential construction could be the Ballston Metro stop, where a new shopping center and office complex is planned nearby. Said Tom Parker, county head of economic development: "That force of retail activity is going to be extremely attractive for people who are looking at Arlington as a new residence."