An administrative law judge recommended yesterday that Attorney General Griffin B. Bell approve a proposed joint-operating agreement between the separately-owned Cincinnati Enquirer and Cincinnati Post newspapers.

Approval of the joint agreement, which would merge the commercial operations of the two papers but leave the news department as separate ventures, was recommended by Judge Donald R. Moore because he felt the Post would fail financially without the arrangement.

"The past operating results of the Cincinnati Post and those reasonably to be expected in the future are such as to demonstrate that it is in probable danger of financial failure," Moore wrote in a 142-page report.

Under rules of the nine-year-old Newspaper Preservation Act, certain antitrust restrictions can be waived when the Justice Department determines that a joint operating situation is needed to preserve two editorial voices in a city.

Although the law has been used only once, for the 1974 agreement joining business sides of the Time and Daily News in Anchorage, Alaska-a merger that is now being dissolved-newspaper has set up similar operations in 22 cities before enactment of the law and were allowed to keep them in place.

Both Cincinnati newspapers have daily circulations of about 190,000 but the Enquirer publishes alone on Sunday, with a circulation of 290,000. The Enquirer publishes in the morning and the Post in the afternoon Monday through Friday and in the morning on Saturday.

According to submission to the Justice Department, the Post had lost $11 million since 1970. The Post has been a victim of the difficulties that have plagued inner-city afternoon papers in recent years, such as the increased cost and difficulty in delivering the paper in traffic-congested city streets and the growth in viewership of evening news programs.

Evening newspaper circulation has dropped more than 2.3 million copies nationally for the past five years, while daily and Sunday circulation has been increasing slowly.

Moore, a Washington lawyer and former newspaperman, said in his report that the weekly newspaper competition for circulation in Cincinnati peared to be stronger than in most cities, furhter hurting the Post's chances.

The post is owned by the Scripps-Howard chain, which has said publicly that without approval for a joint operation it will fold the Post.