Maryland's plan to repay thousands of small depositors at Old Court Savings & Loan Association in April will be delayed at least until May, while one of the defunct thrift's largest depositors challenges the effort in court, Gov. Harry Hughes predicted today.

Hughes, speaking at his weekly news conference here, said that Robert C. Murphy, chief judge of the Maryland Court of Appeals, had agreed to expedite the challenge to the plan, which would initially pay back about half of the Baltimore thrift's 34,497 customers. But Hughes said the dispute could not be resolved in time to meet the payment schedule he set early this year.

"Assuming that the court doesn't have any delay . . . and assuming that we win, you are probably talking the first part of May" before 17,103 Old Court customers gain access to their $26.4 million in deposits, Hughes said. Most of those depositors are the association's smallest account-holders, persons with deposits of $5,000 or less. Depositors with larger accounts would receive the bulk of their money over the next four years as Old Court's assets are liquidated, under Hughes' plan.

The repayment plan, which is to be funded initially by $100 million in state transportation money, has been challenged by the United Wire Metal & Machine Fund, a New York-based union pension fund that has about $17 million tied up in Old Court.

In oral arguments this month before Baltimore Circuit Court Judge Joseph H.H. Kaplan, attorneys for the pension fund advanced two main reasons why the judge should reject the depositor repayment plan. First, they said, deposits should be distributed on a prorated basis, with each depositor receiving an identical percentage share of frozen funds. For example, in a 10 percent distribution, a holder of $1 million could receive $100,000 while a person with $1,000 in Old Court could get $100.

Second, the union's lawyers contended that Hughes' repayment plan violated the equal protection provision of the U.S. Constitution, effectively discriminating against Old Court's largest depositors.

Kaplan, who is overseeing the state's receivership of Old Court, rejected their arguments, ruling that there was a rational basis for the state to ease its financial and administrative burden by distributing government funds to help as many Old Court depositors as it could. The union has appealed the case to the Maryland Court of Special Appeals.

Fred A. Schnur and John McHale, leaders of a statewide organization of S&L depositors, said the group considered joining the pension fund in its suit and then decided against it because of the delay the suit is certain to cause in the repayments.

"It was more important to get the money out," said McHale. "People are awfully discouraged by this delay. Just when their hopes are up about getting this little bit, along comes this."

Despite the delay the pension fund appeal is almost certain to cause, Schnur said he did not begrudge the union its lawsuit. "They have to do what they have to do," he said. "After a year of suffering, what's another month wait? Nothing in this crisis has been done on an equitable basis."

In other developments today, the governor said he rejected an appeal by Baltimore's state senators for millions of dollars in additional state aid to their area. "I was upset that the request was coming at this late date," said Hughes, who met with the senators Wednesday, 12 days before the end of the General Assembly session.

Some Baltimore senators have threatened to disrupt the planned sale of Community Savings and Loan of Bethesda if Hughes does not authorize the extra state aid.