Fairfax County statisticians have seen the future, and it's vastly different from the one they envisioned just a year ago.

Despite the election of a "slow growth" Board of Supervisors in November, the county's Office of Research and Statistics number crunchers have increased their forecasts of how many people will live in the county in coming years.

Last January, in the county's 1986 Standard Reports, a statistical profile of housing, population, income, development and land use trends, officials predicted that the county's population in the year 2000 would be 791,500. In the 1987 Standard Reports, released Thursday, that figure rose more than 100,000, to 897,560. That is more people than lived in the cities of San Diego, San Francisco, Denver, Miami or Phoenix in the last census.

Similarly, while just a year ago officials forecast 333,024 housing units in the county in 2000, they now estimate that number will be surpassed by 1995 and predict that 376,119 units will be built.

The report, based on figures from January 1987, says there were 704,757 residents and 270,744 housing units in the county last year.

Board of Supervisors Chairman Audrey Moore said she wasn't surprised that the county had revised its estimates so sharply. She said even the new population forecasts are "way underestimated."

"If there's not another zoning application granted, the county's already committed to a tremendous amount of growth," Moore said. She said the only way to adequately forecast and plan for the future is by revising the county's master land use plan.

Officials said the report is based soley on current demographic trends and does not account for potential political swings or policy shifts in the county.

Asked if she could foresee the newly elected board's taking steps -- such as restricting zoning -- that might ultimately reduce the number of people expected to live in the county 12 years from now, Moore said, "What I want to see us have here is balance {between public facilities and development}, and I'm not going to predict how we'll get that balance."

The report says 1987 forecasts are higher than previous projections because of expansion in the region's economy and housing markets in the 1980s, a high growth rate in housing inventory since 1983 and "a high growth path for the county's basic economic sectors -- manufacturing, business and profesional services, and communications."

The report says that the county will be "residentially built-out" around 2000, meaning there will be no more clear ground on which to build more houses.