Democrat Winfield M. Kelly Jr. and Republican Lawrence J. Hogan, who have spent most of this month calling each other liars, agree on at least one point as the Prince George's County executive campaign enters its final phase: the race is growing closer by the day.

Kelly, in the unexpected position of being the underdog incumbent at the start of the campaign, has exhibited a new-found optimism this week, saying that his performance on a series of television debates and a 30-day radio advertising blitz will help him catch Hogan by the Nov. 7 election.

Hogan, whose private poll in late September showed him leading Kelly by a 25 percent margin, now believes that his better-financed opponent has cut the lead to the point where "it's quite possible that Kelly could win."

Although Hogan has maintained all along that the race would be closer than his polls indicated, it has been only in recent days that Kelly and his advisers acted as though they believed it themselves.

"You have to remember that early last summer we thought Winnie had the election locked up," said John A. Lally, Kelly's top aide. "Then, all of a sudden, the old heavyweight champ (Hogan) steps in. It left everybody around here stunned for awhile. We went from the sure winner to the underdog so fast, it was really frustrating."

The Kelly camp was still suffering from bouts of depression and uncertainty, Lally said, until the two candidates finally squared off at a television debate two weeks ago. "When Kelly stood there toe-to-toe and danced with him, when he realized that he could stand in there with Hogan, which is not an easy thing to do, it made him feel good. He's been elated and up ever since."

Hogan, on the other hand, believes that nothing has been gained or lost by the debates. "They haven't illuminated any issues, they've just had us yelling at each other," said the former congressman. "In my opinion the debates have been totally counter-productive."

There is one set of numbers that according to Hogan explains Kelly's resurgance: Kelly has raised more than $200,000 to spend on the campaign; Hogan less than $80,000. "There's no way to minimize the impact of the advertising the kelly can run with that money," said Hogan.

Kelly, the 42 year-old millionaire businessman who has made "New Quality" the theme of his administration, began running radio spots on five Washington-area radio stations Oct. 5 and will keep running them every day until the election, at a cost of more than $40,000.

The Kelly radio ads are similar in tone and content to ones he ran several months ago, at a public expense of more than $100,000, to promote economic development in the county. They stress a back-to-basics school system, lower crime rate, and reduced property taxes.

Hogan's media campaign so far has been limited to a three-day radio blitz beginning the day after the Sept. 12 primary and full-page advertisements that have run once each this week in the Prince George's Journal, Washington Star and Washington Post.

The Hogan newspaper ads being with the banner headline: "Can you believe what Kelly says about taxes? No!" They list a total of 18 tax proposals Kelly has supported since he took office. Hogan had to run a correction for the ad in The Washington Star because it said the list was of taxes that Kelly "tried to impose on us this year," rather than over four years.

The tax list is one of the issues that Hogan and Kelly have been fighting over in a manner that prompted Kelly, in a lighter moment, to liken the arugment to the "Liar, liar, pants on fire," grammar school taunt. At a debate last week kelly said he had not supported all the taxes on Hogan's list, a denial that prompted Hogan to call Kelly an "out and out liar."

Although the public record and newspaper clippings show that Kelly at one time or another did speak in support of or attempt to impose every tax on the list-ranging from a cat tax to a vehicle tax-Kelly argues that he never thought of implementing all the taxes. Futhermore, he claims that most of the "nuisance" taxes on the list were developed in an effort to lower the property tax.

Kelly has accused Hogan of lying about another issue-the duplication of services in the police department Hogan, who claims that by eliminating duplication he can cut the county budget, has often said that the police department budget includes more than $3 million for the administration of police purchases and that all of that money could be saved by simply merging police purchasing with a central purchasing department.

The budget shows, however, that of that $3 million, only $100,000 went to ward administration, with the rest going to actual purchases for cara, gasoline and repairs.

The two candidate have the same explanation for what they believe to be the deceptions of the other "Winnie's desperate," said Hogan. "Larry's getting scared," said Kelly. And, from Lewis Helm, Hogan's campaign spokesman: "I guess all this means it's getting close."