President Reagan has been made an honorary member of the venerable Society of the Cincinnati, and there is murmuring in the ranks.

Not, you understand, over the fact itself, for the society's 2,800 members, descendants of officers in the Continental Army, tend to be conservative Republicans. The problem lies in how it was done.

There also is the question of precedent. No American ever has been elected an honorary member of the society at large.

In two centuries, only three men, all French, have been elected to honorary status in the general membership: Marshal Joffre, Marshal Foch and Giscard d'Estaing. Another Frenchman, the Marquis de Bouille', was named an honorary member of the French chapter, and various chapters from the 13 original states have elected 11 presidents, from Zachary Taylor to Harry Truman, to their own rosters. Three presidents--George Washington, James Monroe and Franklin Pierce--were hereditary members.

This May, the society will mark its 200th anniversary with its triennial general meeting at West Point, N.Y. Some members thought it would be nice to make Reagan an honorary member before that, on Washington's Birthday, Feb. 21. So the standing committee, which meets every six months, took it upon itself to elect Reagan Oct. 16.

The bylaws state that "the business and affairs of the society shall be managed during the interim between triennial and special meetings of the society by a standing committee." Some members believed the committee, whose normal function is to sign checks and handle other mundane details, went far beyond its mandate in taking such an important step. Some felt it was not a very dignified way to induct the president.

"At least," said Fred Hunt, a Massachusetts delegate, "the general membership could ratify the action at the May meeting. Personally, I would have made him a member of a state society, say the Maryland chapter, which plans a big do at Annapolis for the bicentennial."

The idea of honoring the president seems to have arisen after the White House suggested holding a reception to celebrate the society's anniversary. Later, the society's president-general, John S. Dumont, wrote to the members announcing that the presidential reception will be Feb. 21 at Anderson House, the society's mansion on Massachusetts Avenue. Guests will be limited to 120 by the size of the ballroom. They will be presidents of the state societies and members of the standing committee and their wives.

Only men may belong to the Society of the Cincinnati, named after Rome's celebrated citizen-soldier Lucius Quinctius Cincinnatus. They are descendants of the 5,000-plus officers who served three years with the Continental Army (not the militia) or had certain other qualifications. Only one descendant of an original officer may belong at a time.

In its earliest years, while it was lobbying Congress to pay the officers' back salaries--and while the army still was massed at Newburgh, N.Y., a putative threat--the fear rose in some quarters that the group might be trying to form a new aristocracy. It was suggested, in fact, that George Washington be made king, but he refused. Over the years, the society has made its name for its good works and its remarkable Revolutionary War library.