The St. Louis school superintendent, the number two official in the Montgomery County system and acting D.C. schools chief Andrew Jenkins are among 12 semifinalists to succeed Floretta D. McKenzie in the top spot in the District's public schools, school sources said.

A 10-member search committee, appointed by board member R. David Hall (Ward 2), last week approved the winnowing of the 51 applicants to succeed McKenzie, who left office Feb. 5 to form an education consulting group. A new superintendent is expected to take over the 87,000-student system in July.

The committee has sought to keep its recommendations secret until April, when it expects to complete background checks and interviews. But sources on the committee and the school board said the candidates who made the first cut include:Jerome Jones, the St. Louis superintendent and the only large-city schools chief to apply for the D.C. job. Jones, who has also been superintendent in Stamford, Conn.; Providence, R.I., and Essex County, N.J., is a former D.C. schoolteacher. In 1986, he was one of three finalists for the top spot in the San Francisco system.

Acting D.C. chief Jenkins, the former D.C. deputy superintendent who has begun his interim tenure in a highly public fashion and plans to stay in the spotlight. He and board President Linda Cropp (Ward 4) will hold a news conference tomorrow to announce "a major initiative to rally for the school budget."

Paul Vance, deputy Montgomery superintendent. Vance, a longtime county school administrator, is in charge of the system's day-to-day operations.

Carlos (Skip) Sasse, a "roving principal" for the Florida Department of Education who specializes in dropout prevention. He is a former high school principal in the Fort Lauderdale area.

Jenkins and Jones were among the seven finalists in the District's 1981 search, which ended with the selection of McKenzie.

One prominent candidate who reportedly did not make the cut was James Williams, a school administrator in Dayton, Ohio. A former principal of Cardozo High School in the District, Williams has considerable support on the board and was expected to be a strong contender.

Some board members say that Hall, a former board president who is managing the search, could emerge as a 13th candidate.

Hall said that although he believes he would do a good job as superintendent, he is not seeking the position. He has, however, told colleagues that he is willing to be drafted. Hall is a real estate broker who formerly ran the D.C. Street Academy, an alternative high school.

Committee members interviewed during the past few days were less than enthusiastic about the current crop of candidates, including many of the semifinalists.

The committee's first cut was based on a mathematical ranking of all applicants based on their administrative and educational experience, leadership, publications and community relations. Candidates who scored at least 70 out of a possible 101 points made the grade; several of the 12 under consideration scored only slightly above 70.

Dissatisfaction with the response to the first set of advertisements for the $85,000-a-year position led the board to extend its application deadline to March 15. Candidates who file resumes in the extended period will be considered separately; the search committee may add to the list of finalists in late March.

Despite a second advertising campaign, Hall said, no new applications had been received as of Thursday. Although the school board had planned to spend $2,000 for advertising the position, the search committee has already spent $26,600 on ads in education journals and newspapers in Washington, New York, Los Angeles and Chicago.

William Simons, president of the Washington Teachers Union and a member of the search committee, said he has been calling friends and urging them to apply. But he said, "I have not gotten any affirmative responses so far. Flo {McKenzie} would be a hard act to follow and a number of people told me they don't want to be in that position."

Board member Eugene Kinlow (At Large) said, "If you have five top-flight people, you're in good shape. They don't have to be large-city superintendents if you have strong deputies in the pool."