he Justice Department today sought to clarify the significance of its anti-trust suit announced Wednesday against the Tribune Co. and its wholly-owned subsidiary, the Sentinel Star Co. of Orlando.

The suit, filed in U.S. District Court in Orlando, alleged that the acquisition by the Sentinel Star Co. in October, 1980, of three weekly papers and two weekly shoppers was anti-competitive in violation of Section 7 of the Clayton Act. The department is seeking divestiture of the weekly papers.

In its suit, Justice claimed that the acquisition gave the Sentinel Star a virtual lock on print advertising in Osceola County.

According to the suit, in 1979 prior to the merger the Sentinel (daily circulation: 168,000) controlled 64 percent of the print advertising, the five weeklies had the other 36 percent. The suit further alleged that the six papers controlled 60 percent of the total advertising dollars spent in the county.

What troubled members of the newspaper industry was that Justice seemed to be laying new antitrust ground by challenging for the first time the acquisition by a daily of a weekly or a shopper.

Moreover, a remark in Thursday's Wall Street Journal, attributed to Alan Marx, a Justice attorney, seemed to signal a new aggressiveness by the department. If the government wins the case, he said, it should serve as a strong signal to newspaper publishers that buying up competing weeklies won't be tolerated.

But today, those remarks were tempered a bit by Abbott Lipsky, deputy assistant attorney general in the antitrust division.

"The acquisition of a shopper by a daily can be--but need not be--anti-competitive, depending on the circumstances of the particular market," said Lipsky. "We believe we can establish that the acquisitions were anti-competitive in this case," Lipsky said, adding, "the case has no particular significance beyond that."

The five weeklies acquired for $4.14 million are the Kissimmee Gazette and the St. Cloud News, a weekly free paper called This Week in Osceola County, and the Osceola Shopper and the St. Cloud Shopper.