For two hours on Saturday afternoon next month, Jimmy Carter will sit at his desk in the White House Oval Office, with Walter Cronkite by his side, answering telephone calls from around the country on a live radio broadcast.

The unprecedented program, to be broadcast from 2 p.m. to 4 p.m. on March 5, will be called "Ask President Carter," and is part of Carter's overall attempt "to stay close to the American people."

White House press secretary Jody Powell, who announced details of the program yesterday, said the telephone calls will be accepted on a special tollfree line to be installed at the White House by CBS.

The caller's questions and comments, and the President's responses will be broadcast live on CBS radio and made available to other radio and television networks after the program, he said.

The presidential radio talk show is the most startling and innovative suggestion that was contained in a memo to Carter this week from a so-called "People Committee" within the White House.

Other suggestions included that he make use of the sophisticated communications facilities of the National Aeronautics and Space Administration for live, two-day discussions with various forums such as business conventions, around the country, each month randomly select American families to attend official White House functions and have dinner with the First Family, and hold a series of White House luncheons and conferences featuring relatively unknown people with "innovative" ideas in various fields.

The radio talk show was originally suggested to the White House by CBS News President Richard S. Salant. The participation of Cronkite, the CBS television news anchorman who is one of the best known personalities in the country "just evolved," according to Powell.

Barry Jagoda, Carter's television adviser, said there will be no screening of calls for content but that there will be a seven-second delay in broadcasting remarks that are made. This is a standard device used on live call-in programs to eliminate obscenity or other objectionable material.

Cronkite's role on the program will be to act as the moderator, telling Carter the name and resident of each caller, Jagoda said.

When calls come in, Jagoda said, CBS personnel answering the phones will ask each caller his name, telephone number and place of residence. They will then call directory assistance in the caller's city "to make sure people are using their real names."

If so , the person will be called back by the White House, put on hold and eventually put through to the President, he said.