Hemisphere National Bank disclosed yesterday its chairman, two other directors and its largest stockholder have agreed to sell their 59 percent share of the bank to a group of investors headed by 31-year-old Jeffrey Cohen for about $3,150,000.

Cohen earlier this week revealed he has signed other agreements to make a public offer to buy all the stock of Bank of Columbia for $7 million and simultaneously to sell his 29 percent interest in District of Columbia National Bank for a reported $3 million. Less than a year ago Cohen bought the stock for about $40 a share and reportedly will sell it for $60 a share, a profit of about $1 million.

Cohen has so far refused to disclose who his partners are in the deals, but will have to identify all of them to obtain approval on the sale of the sale by the Comptroller of the Currency.

At Hemisphere, Cohen has obtained options to buy stock now owned by Leveo V. Sanchez, president and chairman of the bank, and interests Sanchez represents including director Peter B. Davis. Cohen also has options to buy shares owned by Hemisphere board member Angel S. Roubin.

In a complex transaction Sanchez and Roubin also have agreed to buy and resell to Cohen stock owned by Nestor Julio Garcia, an Argentine banker and Hemisphere's biggest stockholder.

The three-way bank stock trade is believed to have been inspired by the expectation that Congress will soon repeal federal restrictions on interstate banking and allow banks to conduct business in neighboring states.

If that happens, Washington bank charters will become much more valuable, because the easiest way for a Maryland or Virginia bank to break into the District market will be to buy a small local bank. Stocks of most local banks have already jumped in value in anticipation of the change in regulations.

Hemisphere was organized largely by Hispanic business people to serve Washington's growing Spanish-speaking community. Cohen's take-over plan calls for Sanchez to remain president of the bank until March 1982.

If the Cohen deal goes through, Hemisphere will become the second minority-owned bank in Washington whose control has shifted out of minority hands. The struggling Diplomat National Bank, organized by Asian-Americans, recently was taken over by veteran Washington banker Leo Bernstein, formerly vice chairman of National Savings and Trust.

With deposits of $20.5 million, Hemisphere ranks 14th in size among Washington's 17 banks. Bank of Columbia is 13th, with $44 million in deposits. Diplomat, with deposits of $8.6 million is currently the smallest, behind Women's National Bank with $9.5 million and American Indian National Bank with $14.9.

The agreements to give Cohen and his associates control of Hemisphere call for Roubin and Sanchez to sell Cohen's group 89,056 shares of the bank's stock for $35.40 a share. Sanchez, Roubin and their associates own 52,781 shares and they are to buy the 36,275 shares now owned by Garcia.

The announcement said Sanchez and Roubin have agreed to pay Garcia $963,000 for his stock, the equivalent of $26.55 a share, then to resell those shares to Cohen.