On Dec. 28, President Reagan displaced the Republican he had appointed three years ago as chairman of the Consumer Product Safety Commission and replaced her with a Democrat more to the White House's liking. The change was made over the protest of the Republican senator who is chairman of the committee that is supposed to approve the nominee.

How was it done? By rushing the appointment through before Congress came back.

Nancy Harvey Steorts, a Reagan supporter who organized two candlelight inaugural dinners at the beginning of his first term, had proved to be too liberal for his second, according to congressional sources. But a CPSC source said that her style of management also embarrassed the White House.

Some commission sources have said that Steorts had hoped for a reappointment to the CPSC or another federal position but that she did not win either because some White House aides objected to her activities on behalf of consumers.

Steorts quit as CPSC chairman in November, after her term had expired and there had been no indication that the White House would renominate her. One source said that a White House official told Steorts she would have to leave the agency two days before she held a press conference announcing her resignation.

When Steorts resigned, she specified that her resignation was effective Jan. 5, after Congress reconvened. She says she picked this date arbitrarily. Regardless, the Constitution mandated that the White House nominee to replace her would have to be confirmed by the Senate before taking office.

Immediately, White House sources named CPSC Commissioner Terrence M. Scanlon as the leading contender. Scanlon, a Democrat, had sided with the administration on several key agency votes and strongly favors its goal of a reduced role for the regulatory agency.

But Sen. Robert W. Kasten Jr. (R-Wis.), chairman of the Senate committee that must approve the new CPSC chairman, had his own ideas. Kasten beseeched the White House to consider one of his home-town consumer activists, Camille Haney, as chairman. Although she was interviewed by the White House, Scanlon won. This drew the lines for a potential flap between the White House and Senate.

Somebody in the White House decided to avoid that confrontation by doing something about Steort's resignation date -- namely, changing it, according to commission sources.

On Dec. 28, the White House called Steorts. According to one White House source, Steorts was told that Scanlon's nomination was going to be announced in 15 minutes. To be loyal to the White House, the source said, she was told to resign immediately and swear in Scanlon as the new CPSC chairman. "The procedure was highly unusual," one commission source said.

Scanlon was sworn in three days later on Dec. 31, four days before Congress returned to town. "Whenever the White House does a recess appointment when there are various candidates and, as a result, takes a Senate confirmation out of a loop, eyebrows are raised and, often, tempers flare," said a congressional source. "And tempers flared."

The White House called Scanlon's nomination a "recess appointment." It enables Scanlon to serve for as long as a year without Senate confirmation.

The Constitution provides that the president may make an appointment without Senate confirmation if the chairmanship "happens" to become vacant when the Senate is in recess. But, congressional sources said, this chairmanship didn't "happen" to become vacant -- it was made vacant.

According to commission sources, Steorts fought the White House order and went out "kicking and screaming."

"She was livid," said one commission source, who added that she made several calls to the White House in protest.

Steorts, who is rumored to be considering a job in a Dallas-based grocery chain owned by the Hunt family, denies that charge and said that "if this is what the president wanted to do, I would gladly do whatever was necessary. I was very glad to back my date up to be accommodating to my successor."

Sources say that at about 4:10 p.m. on the last day of the year, Scanlon was sworn in by Steorts, who told him that the job would be a "wonderful challenge."

Three days later, Steorts gave herself a going-away party at the Mayflower Hotel. She invited 1,500 people to the $15-a-person party, which had a cash bar. Only about 100 came.