Now is the time for us to tell a story we have been sitting on for more than 12 years. It concerns Frank C. Carlucci, President Reagan's national security adviser and his choice to replace Caspar W. Weinberger as defense secretary.

The story involves Carlucci's values -- his character, if you will. Here are the details:

By the mid-1970s, Carlucci had risen through the ranks of the career Foreign Service, been director of the Office of Economic Opportunity, deputy director of the Office of Management and Budget, and undersecretary of health, education and welfare. In December 1974, Carlucci's success was capped when President Gerald R. Ford named him ambassador to Portugal.

For all his professional achievements Carlucci's private life was far from serene. By 1974, he was legally separated from his wife and was getting a divorce. Meanwhile, he had developed a close relationship with an administrative assistant he worked with at HEW, Marcia Myers.

According to several sources, Carlucci took Myers along when he reported to Lisbon as ambassador in January 1975. She became his special assistant, with the rank of Foreign Service Reserve Officer, Grade 4. One of our sources said Lisbon embassy employes were quite upset, because Myers' appointment "took a job from someone." Another source told us at the time that the embassy "had to shift people around" to make room for Myers, and "an assistant administrative officer {was} tossed out."

There were misgivings of a different sort back in Washington, where State Department officials feared the Portuguese, among the most conservative Catholics in Europe, would be upset by the arrangement between Carlucci and his female assistant.

Our sources said concern was so great in Foggy Bottom that senior officials asked then-Secretary of State Henry A. Kissinger to intervene. One well-placed source said Kissinger had at least one conversation with Carlucci about the situation.

Several months after he took up his post in Lisbon, Carlucci's divorce became final. He and Myers were married on April 15, 1976.

Why didn't we publish this story when we first nailed it down in 1975? Just as we were about to, we received urgent telephone calls from two high government officials whom we knew and trusted. They pleaded with us not to send out the story, on the grounds that Carlucci's first wife and their two children, already traumatized by the separation and divorce proceedings, would suffer additional emotional distress.

Our callers provided sufficient detail to convince us to sit on the story.

So we elected to sit on the story. Carlucci has since gone on to serve with distinction as deputy director of the CIA, deputy defense secretary and national security adviser.

We believe, however, that the manner in which professional Foreign Service employes were shunted around, so that Carlucci's friend could get a job that others worked hard for, deserves to be aired as he takes over the biggest bureaucracy in the government.