Former State Senator and Baltimore liquor commissioner Joseph J. Staszak pleaded guilty today to mail fraud and tax charges stemming from his ownership of a secret interest in a Dundalk tavern while serving on the city liquor board.

Staszak, a long-time political power broker here, pleaded guilty in U.S. District Court to one count of mail fraud and one count of filing false income tax returns as part of a plea bargain with government attorneys. In returns, 20 other counts against the 63-year-old Democrat were dropped. Prosecuting attorneys asked U.S. District Judge C. Stanley Blair to impose a jail term but declined to recommend a length.

He was indicted March 28 by a grand jury on charges of mail fraud, racketeering and filing a false income tax form. The indictment charged he concealed his financial interest in a Dundalk tavean while serving on the Baltimore Liquor Board.

Staszak originally had pleaded innocent to the charges, claiming he gave up his financial interest in Joe's Tavern when he was appointed to the board.

But Monday, Staszak pleaded guilty to one count each of mail fraud involving the mailing of the bar's liquor license transfer and making false statements on his 1976 U.S. income tax return by understating his income by about $44,000.

"What I did was wrong, your honor, I freely admit that," Staszak told the judge. He said he received profits and exercised control of the bar while serving as a liquor commissioner.

Prosecutors said that, while Staszak transferred his ownership in the bar to his daughter and son-in-law, he "was, in fact if not in name, the owner of Joe's Tavern."

The indictment alleged that Staszak received about $200,000 from tavern operations while on the Liquor Board, which grants liquor licenses and regulates bars, restaurants and other businesses that sell alcoholic beverages.

Starzak used the money for his "personal financial and other benefit," including investments in two oil and gas companies in Texas and a thousand-acre Christmas tree farm in his native Michigan, the prosecutors said.

Staszak was a state senator from 1967 to 1975, when he was appointed to the Liquor Board by former Gov. Marvin Mandel. Gov. Harry Hughes last month decided not to reappoint him to the post when his term ended May 1.