Chairman John T. (Terry) Dolan of the National Conservative Political Action Committee said yesterday his organization is underwriting a $50,000 advertising campaign on local radio stations to "expose the regular and consistent leftist bias of The Washington Post."

"We caught The Post cheating," Dolan said at a news conference. "We want a correction. We can't get one. I believe it's because they think they run this city."

The first series of ads, which are sponsored by the Committee for a Free Press, a new NCPAC offshoot that Dolan chairs, takes the newspaper to task for reporting "falsehoods" about NCPAC's won/lost record in 1982 congressional elections.

"Following the 1982 elections The Post printed five contradictory win/loss records for NCPAC," the ad states. "All five were wrong. When these mistakes were pointed out by NCPAC Chairman John T. Dolan, The Post responded by having Mr. David S. Broder write another article which came up with a sixth contradictory record and an additional seven falsehoods. Although The Post's own ombusdman agrees that The Post reported seven contradictory win/loss records, The Post refuses to run a correction."

In the days after the election, Post ombudsman Robert J. McCloskey has written, The Post did contradict itself. One story said NCPAC had won one race of nine; another one of 14 and another one of 17.

Dolan claimed yesterday that the contradications were evidence not merely of sloppiness, but of the paper's desire "to report the 1982 election as a huge repudiation of conservatism."

In a Post editorial section article last November, Dolan maintained that NCPAC's win record in the 1982 election was 70 percent. He repeated that yesterday.

However, figures supplied by NCPAC yesterday show that the group won one of 36 House and Senate races in which it made independent expenditures totaling $3.1 million. In 137 House races in which the group made smaller direct contributions totaling $250,000, it had 41 winners and 96 losers.

In 51 House races where NCPAC made endorsements but no expenditures, it backed 47 winners and four losers.

Asked where the 70 percent win figure came from, NCPAC spokesman Craig Shirley said it had appeared in Congressional Quarterly. He said NCPAC stood by that figure, but acknowledged he had no idea where it came from.

Dolan characterized NCPAC as having had a "successful" year in 1982 and said The Post's insistence on reporting it otherwise was evidence of bias. "Anytime you defeat an incumbent senator, you are successful," he said. "If we can help replace one liberal with one conservative per election, we'll be happy."