During the presidential campaign of 1976, Johnny Carson offered an explanation of why many voters were unable to decide that fall between outsider Jimmy Carter and insider Gerald Ford: "It boils down to fear of the unknown versus fear of the known." Today in Ohio, where the prospects for a 1986 gubernatorial brawl between one-term Democratic incumbent Richard Celeste and his predecessor and 1978 conqueror, former four- term Republican governor James A. Rhodes, are real. A few politicians think the voters' choice next year in Ohio could boil down to fear of the known versus fear of the known.

How is it that Jim Rhodes, who turns 76 on Sept. 13, could still be taken seriously as a challenger against former Rhodes scholar Dick Celeste, 47, who as a reformer in 1982 won the state house by more votes than any Democrat in Ohio history?

Two reasons: first, since running successfully on a pledge to install higher ethical standards in state government than those of the Rhodes years, Celeste has presided over an administration known, in the phrase of one pro- Celeste newspaper, for its "sleaze factor." Second, Rhodes, who deliberately failed over four terms to develop any prot,eg,es or encourage any line of succession, is a genuine marvel at electoral politics. But as more than a few Republicans concede, Rhodes may be the only GOP candidate Celeste can beat.

At the difficult art of winning elections, Rhodes has few peers. When Franklin D. Roosevelt was in his second White House term, Jim Rhodes was the elected city auditor of Columbus. When Jack Kennedy was in the White House, Rhodes was in the Ohio state house, where he governed as well under presidents Johnson, Nixon, Ford, Carter and Reagan.

Rhodes' record on nonelection days has not been nearly so impressive. A lifelong advocate of low taxes to attract industry, Rhodes governed an Ohio that, in combined state and local taxes as a percentage of personal income, ranked 50th. It was last in spending on state services such as mental health and environmental protection and first in forced school closings -- a tragedy that was averted by Celeste's hefty 1983 tax increase.

And therein lies another problem for Celeste, who, having been beaten by Rhodes in 1978, when Rhodes charged that the Democrat intended to double state taxes, won a 1982 campaign that was notable for its ambiguity on that issue. Once in office, Celeste moved quickly to win passage of a tax increase he deemed necessary to restore the state's fiscal health. Even though a referendum to repeal the Celeste tax increase was defeated in the fall of 1983, the 1984 Reagan-Bush campaign -- in mailings to 3 million Ohio Democrats -- tied presidential nominee Mondale to Celeste as a high-taxer.

If he has to, Celeste could support a tax cut before Election Day. But the ethical problems are not so easily handled. Celeste appointees have resigned, been indicted and been convicted. There are rumors of federal investigations into Democratic fund-raising tactics under Celeste's administration, and there is the reality of a probe of the failure of the poorly regulated Home State Savings, which was headed by one of Celeste's most prominent contributors and fund-raisers, Marvin Warner. Ethically, the Celeste administration may be no worse than its predecessor. But the difference is that Dick Celeste promised it would be different, that he would bring higher standards to state government. His failure to do so has cost him the enthusiasm and the commitment of many citizen-activists and helped bring on an unwelcome primary challenge from former Cleveland mayor Dennis Kucinich.

Like Celeste, Rhodes faces a primary, with state senators Paul Gillmor and Paul Pfeiffer as likely challengers. If Celeste and Rhodes meet next November, one leading Ohio Republican predicts "the most negative gubernatorial campaign in U.S. history." With Celeste and Rhodes both running on the record -- the other guy's, that is -- it would be just that. The fear of the known versus the fear of the known.