LOS ANGELES — The Justice Department filed a civil lawsuit Thursday attempting to block the Los Angeles Times’ parent company from acquiring its main regional competitor, which would give it a dominant market position in two counties bordering Los Angeles.

Earlier Thursday, Tribune Publishing announced that it had the winning bid — $56 million in cash — in a bankruptcy auction for Freedom Communication’s assets. The DOJ responded within hours.

In a news release announcing the lawsuit, the DOJ alleged the Times’ planned acquisition of Freedom’s newspapers, which include the Orange County Register and the Riverside Press-Enterprise, would give it a monopoly that would potentially allow the paper to hike prices and reduce its quality with little consequence from readers and advertisers. The DOJ said Times and Freedom newspapers make up 98 percent of all newspaper sales in Orange County and 81 percent of English-language fare in Riverside County.

“If this acquisition is allowed to proceed, newspaper competition will be eliminated, and readers and advertisers in Orange and Riverside Counties will suffer,” Assistant Attorney General Bill Baer of the department’s Antitrust Division said in the release. “Newspapers continue to play an important role in the dissemination of news and information to readers and remain an important vehicle for advertisers. The Antitrust Division is committed to ensuring that competition in this important industry is protected.”  

Chicago-based investor Michael Ferro acquired control of Tribune Publishing in February and named Justin Dearborn chief executive, replacing the fired Jack Griffin. Times editor Davan Maharaj was promoted to editor-publisher this month. With Tribune’s flagging stock price, rumors have swirled for months about the company selling off its chain of newspapers, which include the Times, Chicago Tribune and Orlando Sentinel. Billionaire philanthropist Eli Broad has long been assumed to be the front-runner if the Times were to go on the market.