In a cluttered campaign office here, a television beams out a picture of Republican Gov. James A. Rhodes with a group of admiring oldsters.

"When you're dealing with senior citizens, we're fighting one thing - loneliness, that's all,' the 69-year-old Rhodes says, artfully shifting the pronoun. Extolling then tells them, "You made Ohio the state it is today and we owe you something."

Another voice takes over, declaring Rhodes "the best loneliness fighter in all Ohio."

As the ad fades from the screen, it provokes giggles from the workers for Rhodes' challenger, Democratic Lt. Gov. Richard F.Celeste.

"I don't know why everyone's laughing," one Celeste worker says. "His ads are better than ours."

Those ads depict Rhodes as a take-charge executive, a people-person and a governor who has tried to solve the state's energy problems.

Celeste's aides know the ads may be crucial. Four years ago, Rhodes came from behind with a stunning media blitz to beat the incumbent., John J. Gilligan. Celeste's people are afraid Rhodes might win this year's election the same way.

As a result, Ohioans are bracing for a massive media campaign in the closing days of the race. Rhodes says he expects to spend $850,000 for his media campaign, and several newspapers have estimated the figure at $1 million. Celeste says he's put $650,000 into his media effort and aides says production and agency costs will drive the total to $800,000.

The campaign pits two of the nation's top media experts against each other - John Deardourff of Washington, who has produced the Rhodes spots, and David Garth of New York, who is Celestes mentor.

Deardourff, the GOP expert, conducted media campaign for President Ford and such Republican governors as James Thompson of Illinois and William Milliken of Michigan. Garth masterminded media campaigns for Mayor Edward Koch in New York City and Gov. Brendan Byrne in New Jersey.

The media blitz here could tip the balance in a campaign that most experts say is too close to call, although Celeste leads by 4 to 5 points in two newspaper polls and reportedly leads by about the same margin in private polls conducted by each side.

Celeste's surge itself is nothing short of remarkable. A year ago, few people knew his name and he was 18 points behind. But the dark-haired candidate, who will be 41 next month, has criss-crossed the state, hammering at what he calls Rhodes' lack of leadership in Ohio's school finance crisis.

"No one has done a lousier job for our schools than Jim Rhodes," Celeste told the Pickaway County Democratic Women's Club recently. "He's flunked every course."

Warming to the metaphor, he added, "We have had more schools close under this governor than all other governors combined . . . It's time we gave our report card to Jim Rhodes and said, "You didn't pass the test."

Celeste, a Phi Beta Kappa Yale graduate, has come a long way from his days as a Foreign Service officer in India, a representative in the Ohio House and a Democratic lieutenant governor largely ignored by the powerful Republican governor.

A Celeste, aide said of his boss, "He's obviously got Rhodes sacred a - less. The question now is whether he blows it in the final days."

In an effort to avoid that, Celeste has stepped up his already heavy schedule of personal appearances: one day last week he shook hands with workers leaving their plant for the day, stopped at a pizza party for campaign volunteers, spoke at the Harper Valley Mother's Club Annual Hill Festival and wound up touring six bars at the Ohio State University homecoming.

But all that may be no more important than two 30-second TV ads flown by Garth to Celeste headquarters last Friday for use this week. They depict Celeste as a man who can solve the school-financing crisis and cut property taxes.

Rhodes too has stepped up the pace of his campaign, but the television ads may hold the key to his reelection Rhodes' campaign manager, Kent McGough, says those ads are designed to show what Rhodes has done for the state and to portray Celeste as a candidate who has failed to come forth with sensible solutions to the state's problems.

One ad attacks Celeste for his timid proposal on school financing. After months of promises to "talk tough" on schools and taxes. Celeste in late September announced that as governor he would appoint a 60-member commission to study the problem and present a financing program for state-wide referendum next June.

Celeste says he personally prefers reducing local property taxes and eliminating them as the primary source of school funding. Instead, he says, he would rely on increased state corporate and personal income taxes. He does not rule ont an overall increase in a person's net state tax burden.

Rhodes would retain the present system, which relies on property taxes for half of the school money.

Behind the issues in the public debate is the question of age. Rhodes is the oldest governor in the nation, although he looks and acts a decade younger than he is.He was first elected to a local officer the year Celeste was born.

Rhodes says the issue is a question of leadership versus vacillation, strength versus weakness. He mocks Celeste as "the young lion, the new leader who opened his mouth to speak" on settling a recent Cleveland teachers strike.

"And what came out? Not a roar, but a whine of indecision - - - Talking about leadership is different from being a leader," says Rhodes triumphantly, adding that he himself actually settled the strike. He warns against turning the state over to "inexperienced hands."

Celeste sees the issue as one of "the old ways versus the new ways. It's the classic struggle - whether we have four mor years of this fellow or take a chance on someone who says, "I'd like to take the state in a fresh new direction.'