Gov. Harry Hughes imposed a 60-day freeze today on most withdrawals from First Maryland Savings and Loan Inc. of Silver Spring, a thrift institution that has lost tens of millions of dollars in savings deposits despite a $1,000-a-month limit on withdrawals in effect since May.

Money can still be withdrawn on deposits made by third parties, such as Social Security funds and payrolls, and the order allows transfers within the institution, such as mortgage payments to First Maryland by those who have accounts there.

Hughes' action, which took effect tonight and came at the request of First Maryland officials, is the second time in five days that state officials have temporarily banned withdrawals at a major thrift institution in the Washington area. On Monday, Hughes stopped withdrawals at Community Savings and Loan of Bethesda for 20 days. Two Baltimore savings and loans, Old Court and Merritt, are under state conservatorship and a withdrawal freeze. The four institutions have about 137,000 depositors combined.

Today's action at First Maryland constitutes a major setback for the Hughes administration, which has been struggling to resolve the state's savings and loan crisis that began with a depositors' run on the state-insured Old Court in early May.

The Hughes administration had appeared to be close to resolving some of its major problems stemming from the crisis. Twenty-one of the state's 102 state-chartered thrifts had received federal deposit insurance, and a pending deal with Chase Manhattan Corp. to acquire three thrifts, including Merritt, plus the expectation that other large institutions will win federal insurance, had led to optimism among state officials.

The Federal Home Loan Bank Board gave three more state thrifts conditional approval for federal insurance yesterday. They are Fairfax Savings and Loan of Baltimore, with assets of $413.4 million; Northfield Savings and Loan of Baltimore, assets $11.9 million, and Sterling Savings Association of Pikesville, assets $3.4 million.

But more than half of the state industry's $9 billion in deposits is still either subject to the $1,000-per-month limitation on each account or frozen altogether.

First Maryland, the state's seventh largest thrift with about $440 million in assets, for weeks had been regarded by state officials as a potential trouble spot. Its president, Julian Seidel, reported in early July that the thrift was as much as $15 million short of meeting a key federal insurance requirement.

In a letter to Hughes requesting the 60-day halt on withdrawals, First Maryland executive vice president Alan Kerxton said the thrift had obtained pledges for new capital and that federal insurance is "attainable within the 60 days . . . . "

Kerxton's letter said that First Maryland had lost $8.9 million in savings withdrawals during August and predicted that "unless deposits are abated, we anticipate an exhaustion of our liquidity before the end of August."

Other sources at First Maryland said that the thrift had lost about $56 million in savings deposits between the end of March and the middle of August, with total deposits falling from $343 million to $287 million.

State officials said today that William Russell, a Baltimore financial consultant who has experience in commercial real estate management, will be brought into First Maryland to manage its day-to-day operations so that Seidel and other officers can concentrate on raising the capital necessary to win federal insurance.

First Maryland also has been searching for a buyer, according to sources in the thrift industry, and it has had talks with Citicorp, the giant New York bank.

M. Albert Figinski, a Baltimore lawyer who has been representing First Maryland in its negotiations with the state, said tonight that he hoped that the 60-day grace period " . . . will give the management of the institution the time to spend their full efforts on getting either Federal Savings and Loan Insurance Corp. approval or another solution. Within the last two weeks there has been substantial progress and it is continuing. FSLIC is obtainable."

But other sources in the state thrift industry took a more pessimistic view. One industry lawyer said that First Maryland had borrowed "millions" from the Maryland Deposit Insurance Fund, the state insurance agency created in May, and that MDIF had forced the thrift to accept Russell as its day-to-day operational director.

First Maryland, which like a number of state-chartered thrifts grew rapidly during the early 1980s, last year drew the attention of the Maryland Savings-Share Insurance Corp., the private insurer that was replaced by MDIF during Maryland's thrift crisis in May.

Last August, MSSIC officials directed First Maryland to reduce its commercial lending because of violations of guidelines that limited commercial loans to 40 percent of an institution's assets. During 1984, First Maryland's commercial loans went as high as 74 percent, according to MSSIC records.

This week, current and former employes said that the thrift during at least the last year and a half repeatedly allowed some commercial depositors to overdraw their accounts and that total overdrafts often reached hundreds of thousands of dollars.

Documents obtained by The Washington Post, for example, show that on July 25, 1984, seven commercial account holders had total overdrafts of more than $300,000, including some that had been covered by the thrift for several weeks. That amount included a $150,000 overdraft by Cambridge Mortgage, a South Carolina firm that is one-third owned by First Maryland.

Seidel was out of town today and could not be reached for comment. Kerxton declined to comment, and Figinski said he knew of no overdrafts.

State officials have complained privately for weeks that Seidel was being unrealistic about his institution's chances of getting federal insurance, and they have repeatedly prodded him to boost the thrift's capital or find a buyer.

Francis X. Pugh, an assistant attorney general who serves as counsel to MDIF, said today, however, that First Maryland "has a couple of plans they are pursuing, and if either one of them works, they'll be okay."

As the freeze order was being prepared yesterday afternoon, it was business as usual at First Maryland's Rockville and Silver Spring branches. Customers, unaware of the imminent freeze, arrived every few minutes in small numbers.

Lisa Wilson, a hotel clerk, withdrew $1,000 a half-hour before the Rockville branch closed, leaving only $3 in a checking account. She said she was relieved to have her money in hand.

"I do not like them at all," she said of thrift institutions, adding that she had moved her funds to a conventional bank.

A customer at the Silver Spring branch, also unaware of the governor's order, vowed to be more timely in withdrawing her monthly $1,000, which she was applying to a home mortgage. "I really don't want to lose it," she said.