The issue of a much-ballyhooed "New Downtown" for Arlington could be decided by the County Board next Tuesday when it is scheduled to vote on plans to transform the aging Parkington Shopping Center into a "Ballston Galleria" shopping mall and office complex.

Technically, the board is slated to vote on zoning and land-use changes that would permit higher densities at the site of the projected $100 million complex, at the interesection of Wilson Boulevard and Glebe Road, and on a site plan for the development.

But most of the 8 p.m. hearing at the Courthouse is expected to be filled with debate over whether the county should supply financial aid to the project. As proposed, the county would float almost $24 million in revenue bonds to improve and expand to eight stories the now five-story parking garage behind the Hecht Co. department store.

May Centers Inc., the St. Louis-based firm that owns the 13.1-acre triangular site as well as the Hecht store and the garage, says its plans to revitalize the center would not be feasible without county aid.

"I expect we're going to have to put out some money before money comes in," said County Board member Ellen M. Bozman, reflecting the sentiments of her board colleagues. "But I wouldn't want to go into this if it shows we're going to be losing money year after year."

By county estimates, the complex would yield $3.5 million in taxes annually in its first decade and would support 3,700 jobs. In addition, a revitalized Parkington is viewed as crucial to the economic redevelopment of the nearby Ballston area, which already is undergoing a transformation from aging homes and struggling businesses to a trendy town house community with more affluent residents.

Besides money for the garage, May Centers also wants the county and state to make nearly $3.4 million in off-site improvements, including widening Glebe Road from four to six lanes. The long-planned widening already is at the top of the county's list of state-supported capital improvements.

The revitalization proposal--which calls for an enclosed, three-story shopping mall with three office buildings on the site--generally has been widely acclaimed by civic groups and most local merchants in the surrounding area, and by the Arlington Civic Federation, an umbrella group of county-wide civic associations.

But all have said some people have expressed reservations about whether the county should help a private developer, and about the long-range implications of such aid for future developments and for the county's bond rating.

The greatest controversy, however, seems to be over the tax-exempt revenue bonds, which would be the first issued in Arlington. Under such a plan, revenue from the 3,000-space garage, instead of the taxpayers, would pay off the construction and operating costs of the garage over a 40-year period.

The county, which does not need voter approval to issue revenue bonds, would not be legally obligated to pay off the bonds, but both county officials and private citizens have raised questions about its "moral" obligation to do so.

Many have urged the creation of some type of debt service reserve or "sinking fund" to assure bond buyers of the bonds' stability. Anton S. Gardner, the county's budget chief who has acted as county negotiator in Ballston Galleria talks, said such a fund is being planned.

Gardner said the County Board would be asked to consider passing a "deficiency make-up resolution" to "pledge to earnestly consider"--and urge future boards to do so--an appropriation to pay off the debt if revenues from the garage are insufficient.

Without such a safeguard, Gardner said, "there might be hell to pay."

County and May Centers officials spent most of last week in St. Louis, poring over the details of the project, which will be unveiled tonight at an 8 o'clock meeting of the Committee of 100, another civic organization, at Marymount College.

Donald Ingold of the Wilbur-Smith Co., hired by the county as a consultant on the bond-issue question, is expected to announce at the meeting that he has told the County Board the garage project is "pragmatic from a traffic point of view and is economically feasible," Gardner said.

"The consultant has said that the bond issue can be structured in a way that the county will not likely have to make any payments," he said. "Revenue bonds seem to be the only feasible way to do it. But the precise nature of the bond structure will be worked out as we negotiate their sale in the fall, and will depend on what the market rate is."

Gardner said the consultant, calculating the "worst possible cases" of interest rates, has recommended that the county consider floating $21 million in short-term bonds for four years at 10.5 percent interest, then refinancing the bonds with a $24 million issue at a long-term rate of 14 percent.

On Tuesday, the County Board will be voting on a May Centers plan to remodel the Hecht Co. store and build a three-story mall that would have space for 100 retail shops and another, as yet undetermined, department store.

The proposal also calls for a nine-story office building atop the mall and a 12-story office building at the tip of the triangle. A third 12-story office building, proposed for the Glebe and Carlin Springs roads intersection, would be built later and is not up for review on Tuesday.

Besides the high-rises, a small park would be built near the triangle's tip and a pedestrian overhead walkway would be constructed across Wilson Boulevard near Randolph Street.

Should the County Board reject any part of the plan, May Centers could build seven-story office buildings on the site, under the current zoning.

"In the long range, it would pay the county to do it," said W.E. Clayton, owner of Clay's Viking Sewing Machine Service, across Wilson Boulevard from Parkington. "We've got to put our confidence somewhere. Anything's worth a little gamble."

Like others who work and shop along the street, Andrew Kolatias of the Parkington Sleep Center and Anthony Duenas of the Revelations shoe store think Ballston Galleria would be good for their businesses. But they are concerned about the quality and kind of stores that might move in.

"I hope they'll bring in some quality stores," Kolatias said. "It would be good for business. I think this is a noble step forward. It's just unfortunate they didn't do it years ago."