Leaders of Maryland's General Assembly say that the financial uncertainty of President Reagan's economic programs have made their own budget-making process so confused that they may be forced to hold a special legislative session later in the year, when they might have a clearer idea of what programs they can cut.

A special session now appears so likely that some legislators serving on the House Appropriations Committee have all but given up trying to pare the state budget now and are urging swift approval of Gov. Harry Hughes' $6.2 billion proposal. Others, such as Del. John Hargreaves (D-Caroline), chairman of the committee, are considering proposals for an across-the-board budget cut. And some Republican legislators say they would support a sales tax increase this year if the Reagan administration budget passes in Congress.

"We don't even know where to start," Hargreaves said when asked about the impact of proposed changes in federal regulations and funding levels. "It is hellishly hard to know how to appropriate funds. We'll pick the numbers and hope to hell they're going to hold."

The nervousness exuded in the budget process in Maryland, where budget-cutting is a cherished legislative ritual, is mirrored elsewhere. Of 45 state legislatures now in session, about 40 are working on 1983 budgets, and many of those still await federal appropriations for the year before.

"Of all the states tangling right now with budgets, the most unanimous response has been, 'How can we plan this thing?' " says Mary Jo Gallagher of the National Conference of State Legislatures. "The states are in a real period of flux right now."

More states held special sessions in 1981 than in any previous year, Gallagher said, and the trend is likely to continue.

For six weeks, members of House and Senate subcommittees here have listened to hours of testimony on the governor's proposed budget. But their usual hawkeye approach has given way to a sense of resignation that the numbers they scrutinize may be meaningless. So far, only small budget cuts have been approved by the committees, such as $200,000 for special training program for social workers at the University of Maryland.

"I haven't heard a serious proposal for a budget cut yet, and you usually do in an election year," says Sen. John A. Cade (R-Anne Arundel), a member of the Senate Budget and Taxation Committee. "We'll just pass it and hope it sails."

Evidence of the legislators' cautious attitude surfaced last week when the chairmen of the House Appropriations' subcommittees went to Hargreaves to report that they had found no large items to pare.

"We're just hunkering down," said Del. Nancy K. Kopp (D-Montgomery), chairman of the subcommittee on Human Resources. "It's like walking on eggshells. We're examining everything, but we aren't ready to make any wholesale cuts yet."

Kopp is among a group of legislators now openly talking about holding a special session later in the year, perhaps in August when they would know more about the federal budget cuts and their impact on the state. But she and others, such as House Speaker Benjamin L. Cardin (D-Baltimore), admit that a summer session in an election year would not sit well with politicians, particularly if they must consider an increase in taxes or another round of cutting services. And they are also aware that the federal budget may not be resolved by then.

"We could have a lame duck session instead," Cardin said last week, explaining that legislators could be called back to work on the budget in November or December, when about 30 percent of them will have been voted out of office for the next term. Alternatively, legislative leaders say, the General Assembly could approve the governor's budget and then leave it to him to impound funds later in the year if there is a shortage.

"I think that would be irresponsible," says Kopp, reflecting the commonly held view that one of the legislature's top priorities should be trimming the budget. "Someone is going to have to figure out what to do."

Legislators also may have the option of approving a 1.5 or 2 percent across-the-board cut, an appealing option in an election year. But final passage of such a measure seems unlikely, since some key leaders such as Kopp and Cardin oppose it.

As legislators try to predict the effects of the federal 1982 and 1983 budgets, both of which have yet to be approved by Congress, they are also trying to prepare for the possible "swap" of social programs proposed under Reagan's New Federalism.

Already, Maryland stands to lose $200 million in 1983 if Reagan's budget passes, and last week state officials criticized the concept of trading the state's Medicaid program for the federal government's food stamps and welfare programs.

"The swap component of the New Federalism proposal lacks a consistent, credible rationale," says a sharply worded position paper released by the state departments of Health and Mental Hygiene and Human Resources."There is no reason why some programs for the poor should be federalized while others are wholly turned over to the states."

Even Republicans in the legislature who work on the budget are doubtful that the swap could benefit the state. "It's Neanderthal politics," says one leading Republican senator who asked not to be named. "And with $200 million in cuts, the s--- is really going to hit the fan here next year."

Although Reaganomics is the chief reason that the budget process in the General Assembly is dramatically different this year, there have been other contributing factors. The legislature approved enough cuts last year--putting off salary raises for state employes and reducing social services--that some budget watchers say there is little fat left to trim.

"Our agencies are spending at low levels now," said Cardin. "We can't go through more big cuts right away."