Executives of two newspapers merging business and production operations have begun preparing their joint work force and say details of layoffs, advertising rates and prices will be disclosed in the next 10 days.

Chief executives of the Gannett Co. Inc., owner of the Detroit News, and Knight-Ridder Inc., owner of the Detroit Free Press said each newspaper will be better than ever editorially because of government approval this week of a joint operating agreement."The people at the Free Press have only one concern and that is to publish the best newspaper possible," said Knight Ridder's Alvah Chapman, who had promised to close the Free Press if Attorne General Edwin Meese denied the JOA.

"It is my expectation that the Detroit News will continue to be No. 1 and the dominant newspaper in this market," said Gannett Chairman Allen Neuharth. "To do that it will have to be better than ever."

The executive committee of the Detroit Newspaper Agency, which will operate the two newspapers, said Louis A. Weill III, president and publisher of the News, will also become executive vice president of the DNA.

Robert J. Hall, executive vice president and general manager of the Free Press, will have additional responsiblity as executive vice president of the DNA for circulation, production and finance.

William J. Keating, the agency's chief executive officer, said departments will begin moving between the two newspaper buildings on Lafayette Boulevard Aug. 18 and continue through the weekend. Advertising will be in the News building and circulation at the Free Press, while news and editorial offices will remain in present locations.

The first joint publication will be Aug. 20.

Keating said the News will continue morning home delivery in some areas outside Detroit, but Detroit area readers will get only an afternoon newspaper at home. The News' morning circulation in Detroit now is about 80,000, he said.

Total circulation for the Free Press currently is 647,763, while the News' circulation is 688,211.

Because of buyouts and retirement incentives, Keating said there will be fewer than 500 jobs lost from the two papers, which together employ about 4,000.

In a brief exchange, executives made it clear they expect to compete editorially as before.

Free Press Publisher David Lawrence, responding to a question about possible expansion of coverage with new money available under the DNA, said, "On behalf of the Free Press we are not about to tell the Detroit News what we are going to do."

Weill responded, "We're not going to tell the Free Press either."