More than a year after the Fairfax County School Board voted to lengthen the elementary school day on Mondays, easing baby-sitting schedules for the county's many working mothers, money problems may consign the plan to indefinite limbo.

"We ought to right now say, 'Hey, let's put that on the shelf for a few years until things look better,' " said Anthony T. Lane (Lee), the School Board's senior member, who has served since 1972 and who otherwise supports the elementary day plan.

"That appears to me to be one thing that we don't absolutely have to have."

Fairfax is not alone. School officials and board members throughout the Washington region these days are putting on hold planned projects they don't absolutely have to have.

Those educators with ambitions to initiate major changes are finding themselves constrained by empty pocketbooks, as a once-robust economy flattens out and taxpayer revolts impose heightened frugality among politicians.

The situation is different in each jurisdiction, as the fates of individual projects have been complicated by politics, taxpayer petition drives, union battles and other factors.

And some school districts have shied away from big-ticket initiatives altogether in recent years, instead investing considerable money in bolstering existing programs or slower incremental changes.

In the District, where civic leaders last year launched an ambitious drive to overhaul the troubled school system, some of the expensive proposed reforms could be unrealistic at a time when the school board is suing Mayor Marion Barry to prevent a $10 million budget cut.

Because of a bungled enrollment count, the D.C. Council has already slashed the schools' budget request, effectively shelving plans to renovate classrooms, upgrade equipment and expand early childhood education.

And other recommendations such as art, music and language course requirements, junior high school magnet programs and incentive pay may also be unaffordable.

In Alexandria, plans to begin full-day kindergarten in four more elementary schools this fall may be in danger because of looming cuts in state aid. In Prince William County, hopes of expanding alternative schools have been put on hold.

"There are dozens of things we would love to do, that we need to do, that we simply don't have the money," said Prince William Superintendent Edward Kelly. "I see this as being one of the cycles -- hitting reality. The whole program isn't going to go down the tubes. We've got to balance what we've got."

"In hard times," agreed Alexandria Assistant Superintendent Vance Jones, "it's a matter of priorities."

The 1980s were a time of tremendous attention on education reform, and millions of new dollars were poured into local school districts to raise teacher salaries, lower class sizes and otherwise improve instruction. Some districts like Fairfax used the national mandate to launch heralded and expensive new programs, such as teacher merit pay, which tied higher pay to classroom performance.

"We've sort of hit a plateau," said Edward M. Felegy, deputy superintendent in Prince George's County, which in the 1980s undertook a large magnet school program to reduce racial segregation and moved aggressively to improve teacher salaries. "I don't really think we're on the downside, but we're not getting the increments of improvements that we'd like."

Despite the leaner times, there have been few layoffs, and some improvements are still going forward this fall.

For instance, the seven-period day will debut in dozens of Northern Virginia schools in September as a way to let students experiment more with electives such as art and music.

But in Northern Virginia, more bad news may be on the way.

Gov. L. Douglas Wilder is scheduled to present a budget-cutting plan to state legislators next month that may include some significant reductions in aid to local schools for the fiscal year that started July 1.

Depending on Wilder's plans, school boards may have to revisit budgets that have already been approved to find ways to squeeze out millions of dollars.

And in Fairfax, school officials received more grim forecasts last week when the Board of Supervisors tentatively limited the increase in next year's budget. When the county limit is combined with expected state aid cuts -- not including any additional cuts Wilder may propose -- the overall school budget would increase 3.4 percent in 1991-92. According to figures provided by school officials, that would not even cover the cost of maintaining the status quo and a 3 percent cost-of-living raise for employees.

Hedging against Wilder's potential cuts and the new county limit, the School Board voted Thursday to put $7 million in a reserve fund.

In the face of this, some believe any pretense of moving forward with costly initiatives is unrealistic. The School Board voted last July to eliminate early closings at elementary schools on Mondays so that students would have more time in class and parents would not have to make additional day-care arrangements one day a week. But in November, the board postponed the change until September 1991 because of the $9.6 million price tag.

Lane said he will propose that a study committee looking at the elementary day be scrapped altogether because money is tight. Superintendent Robert R. Spillane and School Board Chairman Kohann H. Whitney (Centreville) said it was premature to count out the program, suggesting that the money picture may look rosier this winter.

At the same time, local suburban school officials are fighting a rear-guard action just to protect their current state allocations. Commissions in Virginia and Maryland are studying the educational disparity between rich and poor districts, and local educators are wary that the wealthy Washington suburbs may be seen as a cash cow for poorer areas.

Prince William's Kelly has some advice for his fellow superintendents: "You better keep your hands in your pockets."