The slowdown in new home and office sales will cost Northern Virginia governments millions of dollars in cash, road improvements and land that developers would have built or given to the public as part of their projects, officials say.

What was once a flood of rezoning requests through county offices has slowed to a trickle and so have the accompanying promises from developers to improve roads and give land for school sites in exchange for approval of their projects.

Even some of the improvements developers have already agreed to provide are rolling in more slowly than expected because the projects are getting built more slowly or not getting built at all.

While local governments do not keep totals on the value of "proffers" -- contributions that developers agree to make as part of their rezoning requests -- such donations have played a vital role in expanding and revitalizing the infrastructure of rapidly developing counties. Most new schools and parks are built on land donated by developers, who also fund many sewer and road extensions.

"All of the new roads we've built . . . with the exception of {those funded with} our {1988} bond referendum . . . the developers are building financially with their money," said Prince William Board of County Supervisors Chairman Robert L. Cole.

The effects of the development slowdown are showing up in various ways around Northern Virginia:

Loudoun County received $4.3 million in cash from developers during fiscal 1989, which ended in June 1989, but only $1.15 million in fiscal 1990, said Mickey Poole, director of financial services.

In the Fair Lakes area of Fairfax, "you see a lot of streets that are stubbed, because the developer in between isn't building" the planned office park and the connecting roads, said Shiva K. Pant, director of finance for Fairfax County's Department of Transportation.

Prince William County has begun building roads on a "cash-on-hand basis" rather than assuming that development money will pay the bills when they come due, said Public Works Director Robert W. Wilson. "In tenuous times, we would not want to be betting on an uncertain future," Wilson said.

That philosophy may extend to all major building projects, including schools and parks, in next year's budget, Cole said. "Some existing {plans} may get put back, and new projects might not get on the list," Cole said. "Some citizens may not like it, saying, 'We've waited so long.' But we're not going to go into debt to build it."

In theory, developers finance only those improvements necessary to mitigate the effects of their projects. In practice, local governments rely on developers to pay for badly needed roads and facilities.

Northern Virginia jurisdictions "look to developers to fund the improvements that should be funded by state authorities," said Cate Magennis, director of development for Xerox Realty Corp.

The weak market also is beginning to take its toll on Maryland development revenues and in-kind donations, but such contributions play a much smaller role in Maryland local governments' building plans.

Most Maryland jurisdictions are protected somewhat from the slowdown because they have much more standardized systems for extracting developer contributions than their counterparts across the Potomac. Developers in Germantown, for example, must pay Montgomery a $1,500 impact fee for each new house, said transportation planner Glenn Orlin.

By contrast, each Northern Virginia rezoning agreement is unique, and contributions for schools, fire and rescue, and transportation vary widely from project to project. As the economy has worsened, developers have been more reluctant to donate improvements or cash, further reducing the money coming into Northern Virginia coffers.

"The negotiation processes are much longer and tougher," said Prince William planning director Douglas James. "They're much more resistant to giving anything."

Developers are becoming particularly resistant to agreeing to make or pay for improvements before they build their projects, both developers and local officials said. "It doesn't make economic sense" when credit is so difficult to come by, Magennis said.

Local governments also are losing out on revenue they have already been promised because developers are delaying their building plans. Most developers promise to contribute money or build roads before getting their building permits, and many developers simply aren't getting permits.

In Fairfax, building permits dropped 10.4 percent between fiscal 1989 and 1990, to 27,728, and "Harry Homeowner" addition or improvement permits are making up a much larger percentage of the total, development officials said.

"There's a pattern of putting things into a holding pattern," said Henry Schenke, Fairfax chief of bonds and agreements. "People aren't pursuing {building permits} and if they're not pursuing them, the money's not due."

Local officials lose two ways when developers put off paying their proffers: The money doesn't come in when they expected it to, and because proffers are not tied to the inflation rate, the contributions are worth less by the time the developers pay them.

Getting developers of projects already under way to meet their obligations has also become a problem, according to officials. Fairfax has increased its full-time enforcement staff from two employees to five, but still, " "you've got to do a lot of kicking and prodding" to get developers to deliver on their promises, Schenke said.

Projects that default on their proffer obligations have increased 3 percent this year, said Irving Birmingham, director of Fairfax's Department of Environmental Management.