Several nonprofit organizations that serve the mentally ill, the homeless and the poor in Washington’s largest jurisdiction have created a united front to lobby the Fairfax County Board of Supervisors to preserve current levels of social-services funding, despite pressure from some quarters to ease taxpayers’ burden.

“We recognize that the Board of Supervisors has tough choices ahead of them,” said Amanda Andere, of Fairfax Area Christian Emergency Transitional Services, Inc., or FACETS. She said several private organizations are concerned that the county could cut programs that affect the most vulnerable populations. Andere and several other leaders of nonprofits, including Northern Virginia Family Service, the Alternative House, said their activities often intertwine, and so they wanted to work together to make their case to the county government.

In particular, several nonprofit organizations urged county leaders not to reduce contributions to programs that serve homeless children or fund a pool of money, known as the “consolidated funding pool,” for which nonprofits compete to use through competitive and innovative strategies.

“We don’t want to play the game of ‘Don’t cut me, cut that guy behind the tree,’” said Ann Zuvekas, chair of Fairfax County Alliance for Human Services. She also said that Fairfax County has proven to be generous when faced with a choice between bumping taxes a little higher or reducing needed services. “We are willing to pay more in real estate taxes in order to maintain the quality of life.”

But a taxpayer watchdog organization says rising taxes are squeezing the middle class out of the area’s wealthiest jurisdiction, and that plenty of fat could be cut from county bureaucracy without underfunding social services.

“We have Wisconsin here, even though we don’t have collective bargaining,”said Arthur Purves, president of the Fairfax County Taxpayers Alliance. Purves said that despite the county’s efforts to style itself as well-run and efficient, its government has lavished its employees with generous salaries, benefits and pensions that residents can ill afford. In the past 12 years, spending on pensions and health care for its staff has more than doubled, Purves said.

County officials are well into the process of drawing up a spending plan for the new fiscal year that begins in July. The Board of Supervisors’ budget committee will meet Tuesday afternoon to review some of its options as officials work toward adopting a budget by April 26. On the agenda Tuesday are presentations by the Human Services Council and the Third Quarter Review, which will give the board an idea of what cuts have been carried out in the current fiscal year and what the current economic prospects are for the county. Next Tuesday, the board will also hold a hearing on the effective tax rate. The proposed maximum tax rate would not change but, due to rising home values, it would be a real tax increase of more than 1 percent.

County Executive Anthony H. Griffin has proposed a steady-state budget that would leave the current tax rate unchanged, maintain the same contribution to public schools as last year, and freeze county employees’ pay for another year. Yet Griffin’s proposed budget, which anticipates strengthening home values, would still increase the average homeowner’s tax bill by about $111 a year. His proposed budget also leaves the Board of Supervisors about $30 million to use at its discretion. It could be returned to taxpayers, used to reduce programmatic cuts, or give county employees some pay increases.

But the social services groups say county government is one of the last lines of defense, now that federal spending has come under pressure and Congress could reduce spending on social programs too, such as Head Start. Others say traditional sources, such as donations from corporations, foundations and private citizens, have dwindled following the deepest recession in generations and the poky climb back.

“Foundations are strapped to the limit,” said Judith Dittman, executive director of Alternative House, which serves homeless and abused children. “It is a tough time to be a nonprofit.”

Kevin H. Bell, chairman of the Fairfax County Human Services Council, said the group generally supported Griffin’s proposed budget because of its mostly flat approach to social services spending. But, in a March 20 letter to Chairman Sharon S. Bulova (D) and the Board, Bell noted that rising caseloads mean that even just holding steady could have significant and expensive consequences. He also urged the Board to lay away money for the likelihood of reduced federal spending. He said that if the House of Representatives were to prevail with its proposed cut of $1.1 billion, or 15 percent, to Head Start , the county would suffer a loss of $1.1 million, thereby increasing the waiting list of 1,326 children.

Melissa Bondi, who is campaign director for the Center for Nonprofit Advancement’s and the Nonprofit Roundtable’s regional Think Twice Before You Slice Campaign, said Fairfax County’s challenges are perhaps greater than Montgomery County’s, owing to the different levels of state support for human services. Fairfax County generally receives less in state aid from Richmond than Montgomery receives from Annapolis, she said.

But Purves said county spending has risen out of control. Since fiscal year 2000, the typical Fairfax County household’s tax bill has climbed faster than inflation to $4,901 from $2,407. (A typical household’s home is assessed at $443,551 currently, county documents say.) Adjusted for inflation, the tax bill should be closer to $3,297. Instead, the county has soaked up $600 million a year in spending above the rate of inflation, Purves said.

“The question is — where is it going?” Purves said. And he has some ideas: while both the county’s population and workforce have grown about 10 percent in that time, Purves says spending on county salaries has climbed $141 million, or 20 percent, while spending on pensions has risen $99 million, or 146 percent, and spending on employee health care has jumped $138 million, or 173 percent.

Purves said the extent of the spending increase has been deftly camouflaged, too, by the county’s use of a real estate tax rate that no longer includes the amount spent on stormwater and sewage. That tax adds an extra 1.5 cents per $100 of assessed value, making the effective property tax rate 1.105 per $100.

“They’re playing a shell game with you and me,” Purves said.

Griffin proposed spending $1.24 billion in fiscal year 2012, which begins July 1, or about 1.8 percent less than the previous year’s revised budget, and leaving the tax rate unchanged at $1.09 per $100 of assessed value. The board has already agreed that the tax rate could be as high as $1.09 but it still has the option of voting for a lower rate.

Since fiscal 2009, the county has cut $180 million in general fund spending and eliminated about 500 positions, Griffin said. Last year’s revised budget, largely through reorganizations and pay freezes, came in $40 million below fiscal 2011’s adopted budget of $1.19 billion.