Investigative reporter Clark Mollenhoff voted for Jimmy Carter for president. But that was four years ago, and his love affair ended early, as the title of his new book makes clear: The President Who failed. Mollenhoff's 10th book is the latest effort in a long career of calling presidents on their shortcomings.

Dwight Eisenhower angrily told Mollenhoff to sit down when a tough question the reporter asked annoyed the chief executive at a press conference in 1959.

Mollenhoff accused Richard Nixon of using the "evil doctrine" of executive privilege to hide "mismanagement and corruption" in the White House, this after Mollenhoff quit his nine-month-long job as a special assistant to Nixon. ("It's like the Knight of the Holy Grail becoming a member of the King's Guards," an old friend said of Mollenhoff's surprise agreement to work for Nixon in 1969.

And the Mollenhoff's biography of Gerald Ford was called The Man Who Pardoned Nixon.

It's unclear how John Kennedy eluded Mollenhoff's ire, but among Washington reporters Mollenhoff was known as one tough guy. The Big Boomer, one columnist called him in honor of his great, bass voice that presidents dreaded hearing at press conferences when Mollenhoff wrote for The Des Moines Register and Tribune. "A human battering ram," another journalist wrote of Mollenhoff.

Today the Big Boomer lives in Lexington, Va., and teaches at Washington and Lee University. But he keeps a weather eye on the capital city.

"I voted for Carter," Mollenhoff says, "and I wanted him to do a good job . . . As things went along, I had a few disappointments. I had followed the Ernest Fitzgerald case, you know, and my initial disillusionment was with Carter's failure to follow through on that. [Fitzgerald was the Pentagon employe who suffered bureaucratic reprisals when he blew the whistle on cost overruns on the C-5A aircraft contracts. Mollenhoff says Carter has failed in his promise to protect whistle-blowers from retribution.] Then came the Lance case."

Mollenhoff started looking more closely at Carter and "in essence, began exploring what the president knew and when he knew it. You come to the conclusion that he doesn't know what he's doing or he's intentionally devious -- one or the other or a little of both."

Mollenhoff finds fault with Carter's Justice Department, his civil service reform and his handling of the GSA scandal, among other things.

"He's not a bad man," Mollenhoff says, "but he has a completely flexible conscience. He gets into impossible situations and then figures anything goes to get out of it -- it's for the country rather than Jimmy Carter, which is what all the presidents tell themselves . . . He seems to have picked up all the problems of other presidents. It's like this business of the blatant efforts to disown Jane Byrne in Chicago and say that in some way Chicago will suffer because she won't support Carter. Our presidents have done this kind of thing before, but most of the time they have at least had the decency to deny it."

Footnote: Don't look for advice from Mollenhoff; he declines to give the Big Boomer Seal of Approval to any hopeful 1980 presidential candidate.