A St. Louis-based developer unveiled a long-awaited $100-million plan yesterday to redevelop the aging Parkington Shopping Center in Arlington, contingent upon the state and county contributing millions of dollars in improvements to the area.

May Centers Inc., which owns the 14-acre Parkington tract at Wilson Boulevard and Glebe Road, presented its plans for "Ballston Galleria," envisioned as an enclosed 1.5-million-square-foot retail shopping mall and office complex, to the County Board last night.

Board members said they were generally excited about the plans for the project, which would have almost twice the area of the Seven Corners shopping center in Fairfax County and would provide 3,700 new jobs.

But they cautioned that the county's possible financial commitment must be explored in detail and emphasized a desire that retail space heavily outweigh office space.

The proposed renovation of what is the only major shopping mall in Arlington has been under intensive negotiation for more than two years and is viewed by county officials as crucial to the economic redevelopment of the Ballston area.

Ballston is an area of aging homes and struggling small businesses that is undergoing a dramatic transformation caused largely by its closeness to Metro and the pending opening of I-66. Real estate prices in the area have soared and a younger, more affluent population has been attracted to the area. Massive redevelopment is slated for around the Metro stop.

"We're looking at it Parkington redevelopment clearly as a catalyst for the Ballston area itself," said Anton S. Gardner, director of the county's department of office, management systems and budget, who served as the county's negotiator in talks with May Centers.

The triangular shopping center is a block from the Ballston Metro station and a few thousand yards from planned entrance and exit ramps of I-66. It is a choice site for development that could generate other growth along the Rosslyn-Ballston Metro corridor.

Over the years, county officials say, Arlington has lost substantial revenue as shoppers headed for the larger enclosed shopping malls. Gardner said the redevelopment of Ballston Galleria as proposed could bring the county an average of $3.5 million a year in additional taxes in the coming decade. The first part of the project would open in 1984.

Built in 1951, the Parkington Shopping Center's most prominent feature is the massive, pea-green Hecht Co. department store. It also houses a J.C. Penney Co. store, 19 small retail shops and a five-level parking garage.

May, which is the parent company for Hecht's, proposed to raze everything but the parking lot and the Hecht store, which will be completely remodeled. In place of the other stores, it plans to build an enclosed three-story shopping mall containing over 100 retail shops and, possibly, two more major department stores.

On top of the mall area, the company plans to build a nine-story office building. It also has proposed a 12-story office building with two floors of retail space for the ground-level parking lot abutting Glebe Road.

Other plans call for an expansion of the five-level garage to eight levels, creating twice the 1,500-car space now available and improvements to surrounding roads, sewers, sidewalks, traffic lights and other capital improvements.

Gardner said the company wants the county and the state to pay for off-site improvements, such as road work and sidewalk repairs or expansions, which are estimated to cost $3.5 million.

The cost for refurbishing and expanding the parking garage is estimated at $20 million, which would be paid for through county revenue bonds, Gardner said. The County Board does not need voter approval to issue revenue bonds, a financing procedure in which revenue from the garage would eventually pay off the cost of the bonds.

The County Board is expected to hire a consultant to study the feasibility of making the proposed garage improvements. A May 18 public hearing has been tentatively set for discussion of land use, zoning and site plan requirements.