The 3,500 residents of Fairfax County's Skyline City live in six high-rise towers surrounded by acres of concrete and asphalt.

"We don't even know what a tree looks like," says Ralph W. Morgan, a retired professor who owns an apartment in a 26-story tower there.

Yet when tax time comes, Morgan and his neighbors say Fairfax officials must think they live in the midst of a national forest. This year, $50,000 of the money the county collected in taxes from the high-rises went to collect leaves.

Collect leaves? Except for a few falling from trees planted in concrete pots on a plaza, there aren't any leaves in Skyline City, the residents fume.

"I'm mad, we're all mad," says Margarete K. Anderson, head of the Skyline Plaza Homeowners Association. "We don't get any service at all, and yet we pay for it."

To date their outcries have had all the impact of a leaf falling in the forest. When the residents complain, Fairfax officials turn to a county map and note that the high-rises, near Baileys Crossroads, are in one of the area's leaf collection districts. and, as such, must pay the tax.

"If they're in the district, by law, they must be taxed," says Lurty C. Houff Jr., the county's real estate director. m

Changing the district's boundaries also appears out of the question, says Supervisor Thomas G. Davis III, who represents the area on the Fairfax County Board of Supervisors. "They [county officials] say if they let Skyline City out, they'll have to let others out," Davis explains.

What outrages the residents even more are the 30 percent higher property assessments which the county recently sent them -- an increase which appears to be a record. "I'm afraid it is," Houff admits. "Units have been selling very well. The builders have advertised that the units doubled in value in three years, so a 30-percent increase in assessments in one year seems about right."

As assessments have soared, so have the leaf taxes. That's because the rate is 3 cents for each $100 of assessed valuation. Last year the average leaf tax bill in the county was about $24.

More troublesome to the Skyline homeowners is the fat surplus the county has allowed to accumulate in Fairfax's leaf-collection fund. County officials are urging that the rate be cut from 3 to 2 cents, but Skyline homeowners still would end up paying about $20 each for nonexistent leaf collection because of the rise in their assessments.

For example, Anderson, leader of the homeowners group, paid $23.70 in leaf-collectilon taxes last year. If the rate drops to 2 cents, her bill this year would be $20.80. If the rate stays at 3 cents, it would jump to $31.20.

Anderson's group has called a meeting of residents for tonight, and Supervisor Davis, Fairfax Board Chairman John F. Herrity and Samuel A. Patteson Jr., supervisor of assessments, are supposed to be on hand.

"I'll listen to their problems and see what I can do to help them," Herrity says. But that may not be very much. "It's not a question of opinion, it's a question of law. If you exclude them, you have to exclude everybody else."