Workers have begun removing asbestos materials from the delivery tunnel at the Tysons Corner Center shopping mall, but the potentially hazardous substance will not be taken from public areas of the mall until after the Christmas shopping season, mall officials acknowledged yesterday.

In a project that some shop owners and delivery truck drivers say has been shrouded in secrecy, workers protected by safety uniforms and masks have been clearing the tunnel of asbestos used as fireproofing on metal beams and insulation on steam and hot water pipes for about two weeks.

The project, which thus far has been shielded from public view by security guards in the area, was to shift to other areas of the 144-store Fairfax County shopping center sometime next month. But in a memo distributed to store managers Sept. 25, mall officials said that phase would be delayed until early next year to "avoid any disruption to traditional year-end activity at Tysons."

Hundreds of thousands of Washington area residents do their Christmas shopping at the Tysons Corner Center at Rtes. 123 and 7.

The memo, a copy of which was obtained by The Washington Post, said, in part: "The first phase will deal with nonstore and nonpublic areas. Phase two will deal with store and storage areas."

Charles R. Cope, general manager of the shopping center, said the asbestos problem exists in only 2 percent of the mall area and poses no health risks to shoppers or employes.

An official determination of the possible health risks could be available sometime today, when Fairfax County Health Department officials, who received a complaint from a delivery truck driver Tuesday, inspect the work area. Steven Church, who will conduct the inspection, said the health department had been unaware of the asbestos at the shopping center until the complaint was registered.

"They've kept it very quiet," said one store owner, who asked not to be identified.

Cope denied that the mall management was trying to mislead the public or shopping center employes about the possible health hazard. "We haven't tried to sweep this under the carpet," he said.

But deliverymen who use the tunnel daily to deliver products to the shopping center said they were kept in the dark and that they were exposed to the asbestos while everyone else in the tunnel was wearing protective masks.

One of the deliverymen interviewed yesterday said workers involved in the asbestos clean-up and mall security officials refused to tell him the nature of the problem. "If we're going into a danger area we should be told it's a danger area," said Richard L. Farrell.

"That was under my direction," Cope said when informed of Farrell's comments. Cope said he ordered those involved in the project to remain silent. He said he alerted the store owners to the situation and that anyone else "could have come to talk to me about it."

Asbestos, commonly used as insulation in heating systems for buildings constructed from the 1940s through the 1960s, when exposed and crumbling can release tiny fibers that have been shown to cause cancer and respiratory diseases in those who inhale them. Tysons Corner Center opened in 1968.

The presence of asbestos was discovered at the mall last spring, soon after U.S. Investors Services, Inc., a subsidiary of the Lehndorf Co. of Dallas, assumed ownership of the mall, Cope said.