The plan to build a second regional shopping center at Tysons Corner in Fairfax County may be in trouble even though some economists think there is more than enough demand for another big shopping mall there.

The owners of the 117-acre site where Tysons II would be built asked the Fairfax Board of Supervisors for a six-month deferral on their rezoning application, and it was granted.

"Serious problems have developed in the economics of the site," said zoning attorney John T. Hazel Jr., who represents the owners, developer Theodore N. Lerner and the Gudelsky Co. "The majority of the owners are not interested in a regional center if it means losing flexibility" to develop the land in alternative ways.

Only four months ago, when the supervisors first took up the rezoning application, Hazel said, "This property has sat there for 14 years. We cannot continue to delay development."

When the supervisors in August proposed a deferral of their own to gain more time for working out some complicated problems on financing transportation improvements near the shopping center site, Hazel agreed, but only reluctantly. He said he was tempted to take his chances on a vote up or down.

What the owners want, according to Hazel, is an assurance from the Fairfax County government that if the land is rezoned for a shopping center, they could, at a later time, change their mind and build under the pressent zoning, which permits high-rise apartments and offices and general industrial use.

By the county's own estimate, there is already enough demand for another regional shopping center, one with about 1 million square feet of space, including at least two major department stores. The proposed Tysons II would be developed by Lerner, who built the original (and hugely successful) Tysons center just across Dolley Madison Boulevard (Rte. 123). He also has built other malls in the Washington area. Hazel said it is the other owners, a majority, who are concerned about the project.

"Developing a regional center there requires a man like Lerner," Hazel said. "What if he gets hit by a truck? Anything can happen."

If the owners get rezoning for the $50 million shopping center, they will be committed to spending at least $3 million and as much as $7 million, according to Hazel, for road improvements the county is demanding as a condition of approving the rezoning. Most of the money would go for an elaborate freeway-style interchange at Rte. 123 and International Drive, the road that would connect the two Tysons shopping centers.

If the owners were permitted to change their mind after a rezoning and build apartments, offices and mixed industry, they wouldn't have to put up all the money for transportation improvements. That money is a condition of rezoning for a shopping center. There are no strings attached to the present zoning.

Some of the people familiar with the Tysons II case have described it as a poker game with the county and the landowners trying to bluff each other. The Lerner group, for example, has been reminding the supervisors that the property can be developed at high densities - apartments, offices and industry - and at no cost to the landowners for road improvements. If the county's demands for a shopping-center rezoning are too high, Hazel says, then the property owners will develop the land under the present zoning.

But the supervisors are holding fast to their demands because the market for apartments and offices is slack at the moment. Privately, some supervisors say they are assuming that the Lerner group prefers to build a shopping center.

The stakes for the county are big. If the shopping center falls through, the miltimillion-dollar road improvements that will be needed no matter what is built on the site will be delayed for years because the state would have to bear the entire cost. In addition, the county would lose about $1 million annually in sales tax revenues.