The Chase Manhattan Corp. completed its planned purchase of three restricted Maryland savings and loans early today, guaranteeing 70,000 depositors complete and immediate access to their funds and opening a new era in Maryland banking.

Kevin O'Keefe, a Chase spokesman, said shortly after 2 a.m. today that the deal had been completed.

One industry source said representatives of Friendship, a Bethesda-based association, and Chesapeake, of Annapolis, signed the final sales agreement about 5 p.m. yesterday, leaving only Merritt, a Baltimore thrift that is deeply in debt, to complete the deal.

The final agreement, which came after marathon negotiations, marks a partial rescue of the state government, which for five months has staggered under the weight of the severe thrift crisis.

Chase Manhattan's purchase of the three thrifts and the conversion of their branches to the new Chase Bank of Maryland was approved by the General Assembly, Gov. Harry Hughes, federal authorities and a Baltimore judge within the last 10 days.

"The best place to keep your money is right where it is," said full-page advertisements that ran in Washington and Baltimore newspapers yesterday and today.

The ads are part of a public relations effort that includes planned shuttle bus service to relieve any crowding at the combined 13 branches of Merritt Commercial, Friendship and Chesapeake savings and loans.

Indeed, Chase, anticipating a large demand for some of the $500 million in deposits at the three savings associations, made arrangements to placate customers and reduce an expected drain on deposits from the new bank.

The New York banking giant, through its marketing firms in Rockville and Baltimore, announced it would transfer some New York employes to Maryland.

The Chase Bank said it would set up two telephone hot lines, have expanded office hours until Nov. 5 and pay $25 bonuses on some deposit certificates to smooth the transition.

"We will devote all our resources to ensuring that customers are quickly and conveniently served," said Robert R. Douglass, Chase's vice chairman for national banking.

If the birth of the Chase Bank of Maryland has the immediate effect of freeing millions of customer dollars, it also marks a kind of revolution for the state's banking market, which until now has been protected by laws that barred out-of-state banks from collecting deposits.

By bringing a portion of its $86.3 billion in assets to Maryland, Chase promises to have a profound effect on an already intensely competitive local industry, experts said.

"The market is finite, and if Chase is going to come in and take 20 percent of the market, then somebody's going to lose 20 percent," said G.J. Manderfield, president of Suburban Bank, the state's fourth largest. "There's no question that the presence of a sophisticated lender like Chase will increase competition."

Chase's arrival also has increased the Hughes administration's hopes of resolving the thrift crisis that has preoccupied state government since mid-May.

With Chase's completion of its takeover of Merritt, whose principal owner is under criminal investigation for alleged mismanagement of the thrift, the state eliminated a potential $80 million loss there.

The state was responsible for Merritt's debts because it was the thrift's conservator, and is paying Chase $25 million to take the distressed institution off the taxpayers' hands.

However, the state is still liable for losses at Old Court Savings & Loan of Baltimore, where the debt is estimated to be $175 million, and Community Savings and Loan of Bethesda, which has an estimated debt of $100 million.

State officials say they may be able to sell Community to a giant institution such as Chase, but they are poised to place Old Court in receivership to liquidate its assets.

In a related development, Chase announced that Stanley T. Burns, a 41-year-old Texan and Chase vice president who steered the thrift purchases through a sometimes combative legislature, will be president of the Chase Bank of Maryland.