There between the ads for dining room furniture and the weekly specials at a local food store was an extraordinary 16,000-line treatise on the state of socialism in France.

Published at a cost of more than $100,000, the six-page advertisement in yesterday's Washington Post was the creation of an obscure, ultraconservative organization called the Societies for the Defense of Tradition, Family and Property (TFP). The organization announced later in the day that the broadside was the first in a series of such ads to be published throughout the western world warning that the new socialist government in France portends dangers for the rest of the free world.

TFP was characterized yesterday by several sources as a Brazilian-based Roman Catholic lay organization supported by several wealthy land owners and industrial families primarily in South America. It has chapters in 13 countries, including the United States. The U.S. chapter is headquartered in Pleasantville, N.Y.

TFP established an international office in Alexandria this year to promote TFP concepts and programs. Its two lobbyists, Mario Navarro de Costa and Louis Merizalde, were not available yesterday for comment about the organization. Instead, a TFP office clerk referred reporters to a TFP press release and to the society's book, "Half a Century of Epic Anticommunism," published this year.

The news release said the ads are a "detailed analysis of French self-management" that "clearly show s that French socialism aims at the disintegration of today's society into an anarchic utopia."

Father Enrique T. Rueda, a staff member of the Free Congress Research and Education Foundation, a conservative research group here, called TFP a well-financed Catholic lay organization that produces professionally designed newsletters and background papers on anticommunist subjects as well as such issues as abortion and private property rights.

Recent TFP newsletter articles have dealt with "Violent Youth," cable TV, "Poland on the Brink," and "The Outburst Begins," an article on land reform.

"One might disagree with their point of view," said Rueda, "but the quality of scholarship is from someone who has access to information."

Thomas Quigley, Latin American adviser to the U.S. Catholic Conference, said TFP "considers most of the changes in the Catholic Church and society are bad and is very much oriented to the supposed ideals of the Middle Ages" when kings, the landed gentry and the church ruled the western world.