Chase Manhattan Corp. will buy a Maryland S&L;.

The bank holding company signed an agreement to acquire Bethesda-based Friendship Savings & Loan Assn. Under the pact, the S&L;’s shareholders will retain $20 million of uninsured, long-term, below-market-rate Friendship mortgages as consideration for the sale of the outstanding shares, according to a statement released by Friendship. The proposed purchase needs approval from Maryland and federal regulatory agencies. Friendship has assets of about $307 million.