The budget that Mayor Marion Barry and the D.C. City Council approved last year was viewed by many as an election-year Christmas tree, glittering with funds for city schools, the arts, housing and the elderly.

But tomorrow, when he unveils his austere $2-billion budget plan for fiscal 1984, the newly reelected mayor will begin plucking many of the ornaments from that budget tree.

In contrast to the glowing terms Barry used to describe his "budget for the people" last year, the new budget was described by a top administration official this week as "mean." Even the mayor says, "It's going to be tough."

The new budget proposal may provide the school board with $10 million less than the $336 million it is seeking, according to an administration source. Programs for the poor and unemployed will be frozen or cut. Part-time city employes will be laid off. And funds for Metro and transportation may be slated for cuts.

Even the mayor's top-priority programs to stimulate economic development and create jobs will have to get along without significant increases in spending.

"We're in a time and era when a lot of sacrifices have to be made by everybody, and we have to do our share," said Alphonse G. Hill, the newly appointed deputy mayor for finance who previously was the city's controller.

City officials are scrambling over the weekend to piece together the new budget, which would take effect Oct. 1, for submission to the City Council tomorrow.

The budget is one piece of a much larger financial jigsaw puzzle that officials are trying to assemble to avert deficits and to cope with the harsh realities of an economic recession and declining federal aid to the city.

While they race to finish the new budget, city officials also are immersed in pruning the current year's budget to stem a projected $110 million deficit brought on by a sharp decline in revenues and excessive spending by city agencies.

The mayor has pledged that neither the current budget nor next year's would include major tax increases or layoffs of permanent city employes. He also promised to increase spending for the criminal justice system, in a bid to reduce the District's crime rate by 8 percent this year.

Ivanhoe Donaldson, the new deputy mayor for economic development and a top adviser to Barry, said Friday that the mayor isn't wavering in his opposition to a major tax increase this year. However, he said Barry might have to reassess his position later this year if the recession continues and revenues continue to flag.

"I don't think you should have a tax increase during a recession," Donaldson said. "But let's face it. If the economy keeps going down . . . the mayor will have to look at where he's at."

Jeffrey L. Humber Jr., director of the Department of Finance and Revenue, said his agency is doing everything it can to maximize revenues while assuming no change in the current rates of property and income taxes.

For instance, he said, his department has hired 13 additional tax auditors, to review individual and corporate tax returns, and is also doing a better job of collecting real estate taxes.

Barry's administration is pressing a review of the city's more than 800 service fees, which already has resulted in some increases and could lead to additional increases or even new fees. The city is now charging $20 each for certificate of occupancy permits which previously were issued for free, for example.

The decline in city tax revenues, caused by the recession, has been accompanied by a decline in federal grants in aid to the city to help fund scores of social services--a $20 million overall drop since fiscal 1982, according to a D.C. budget expert.

Federal funding for several programs, including venereal disease treatment, has been sharply cut back, while other programs have been eliminated.

"Over the long haul, that will be a serious problem," the official said.

Even a Reagan administration proposal to increase by $25 million the federal payment the city receives for services to the federal government may be offset by increased charges for treatment of D.C. residents at the federally operated St. Elizabeths Hospital.

Philip M. Dearborn, vice president of the Greater Washington Research Center and an observer of area government finances, said the city's greatest challenge is holding down the rapidly rising costs of Medicaid payments and funds for Metro. Nearly 70 percent of the funds the city spends for transportation goes to pay the city's share of Metro costs.

Dearborn, formerly an aide to Barry, said the mayor may decide to help balance the 1984 budget by not setting aside $20 million next year to reduce the city's long term debt, which currently totals $309 million.

A year ago, Barry's rhetoric was rosy as he released a 1983 budget that called for a whopping 71 percent increase in spending for housing, a 68 percent increase for economic development and a 45 percent increase for job training.

Barry's optimistic budget plan then was greeted skeptically by City Council members and staff, who claimed, presciently, it turned out, that the budget was balanced by unrealistically high revenue forecasts and ignored the city's long-standing fiscal problems.

In his inaugural address last week, Barry warned of the "disquieting new realities" of shrinking federal assistance and growing joblessness that would necessitate city officials to make tough budgetary decisions. Tomorrow, those realities will take shape.