Prince George's County Executive Winfield M. Kelly Jr. yesterday said that The Washington Post's endorsement of his Republican opponent, Lawrence J. Hogan, was based on the same sort of illogic that he occasionally used himself when writing college term papers.

"I remember sometimes that I would list all the points on one side and then reach a conclusion that was exactly the opposite," Kelly said. "That's just what The Post did this morning."

Kelly, who has openly courted the Washington newspaper since he took office four years ago, said he was stunned by The Post's decision to endorse the conservative Hogan.

The Post endorsement, which appeared in Friday's editions, praised Kelly for his efforts to promote economic development in the county and to change the "roughneck style" of the police force by hiring more black officers. It argued, however, that Hogan "might accomplish more" in the area of police department integration because of his "credentials as a conservative and former FBI officer."

"That's the part that's hardest to believe," said Kelly spokesman John A. Lally. "Where was The Post when Hogan was fighting school busing and praising Lester Maddox and saying that police officers should be given the benefit of the doubt when they kill unarmed black suspects? I thought this was a paper with a sense of history."

Hogan aide Lewis Helm, exhibiting his own sense of history, reacted sarcastically when asked how the Hogan camp felt about being endorsed by a newspaper of liberal persuasion. "I don't know how to have this kind of relationship with The Post," joked Helm. "We had a long discussion as to whether we ought to repudiate it or not."

Helm quickly added that Hogan would not repudiate the endorsement, but rather take out a large advertisement in The Post's Sunday editions to promote it. "It establishes Larry's broad credibility more than anything else that could have happened," said Helm.

To many of the 150 county Democrats who gathered at the Sheraton Lanham yesterday morning for a final Kelly pep rally. The Post endorsement confirmed their longstanding belief that the newspaper's editorial writers looked on the suburban Maryland county with scorn and condescension.

Lieutenant governor candidate Samuel W. Bogley, normally and unassuming, soft-spoken man, brought his party colleagues to their feet with a fire and brimstone denunciation of The Post:

"Just when we're about to get our head up, just when we're about to see the light of day, providing the services that are so desperately needed, doing our fair share for the region, paying our dues, a daily newspaper not located in Prince George's, but with real estate in the District of Columbia, hits us right between the eyes. That's what happened this morning."

Kelly, who was sitting on the dais with Bogley, gubernatorial candidate Harry R. Hughes, Baltimore Mayor William Donald Schaefer and state Sen. Steny H. Hoyer, suddenly lunged to the microphone.

"Sam," he shouted. "You're a tiger." "I've been waiting a long time," answered Bogley.

Even Hughes, a candidate who rarely gets excited, was moved by Bogley's speech. "Sam," Hughes said. "I really liked to hear you this morning. You started my day off well."

Hogan, considered a slight favorite in the county executive race, said he told the Post's editorial writers during a luncheon interview several weeks ago that the paper's endorsement would ensure his election. "It's very helpful," Helm said yesterday. "But we think we would have won without it."

Helm speculated that one reason Hogan got The Post endorsement might have been that "Larry was in great form on the day of the interview. There was a surprising rapport that day. It was just the opposite at the Washington Star, where Larry thinks he didn't do as well." The Star has yet to make an endorsement in the race.

Although some county Democrats were depressed yesterday, openly fearful that the Post endorsement would cost Kelly in election, others spoke of the possibility that the endorsement would spark a backlash sentiment for Kelly. "A lot of people out there hate The Post," said one state senator. "It all depends on whether they're the ones who are still undecided."