In Surprise Move, President of Howard University Resigns as Budget Troubles Loom After months of internal rifts and a trustee meeting last weekend, Sidney A. Ribeau, the president of Howard University, announced Tuesday that he would resign at the end of the year. While some of the university's problems were known, the resignation came as a surprise because Dr. Ribeau, 65, who had held the office for five years, signed a contract over the summer that extended his term through the spring of 2015. The university in Northwest Washington is one of the most prominent among the nation's historically black colleges and universities, with a law school and medical school that have produced many top black professionals. But recently, there have been signs of trouble. Last month, U.S. News and World Report ranked Howard 142 among American universities, down 22 places from the previous year - a blow for a university that long ranked among the nation's top 100. Howard's credit rating was downgraded last month as well, from A3 to Baa1. In explaining the decision, Moody's, the ratings agency, cited the troubled university hospital, management issues, an enrollment dip and the effects of federal budget cuts, especially sequestration. Those same problems were cited by the vice chairwoman of the board, Renee Higginbotham-Brooks, who warned in a letter to trustees in April that the university was in serious trouble. "Howard will not be here in three years if we don't make some crucial decisions now," she wrote. In his reply, the board chairman, Addison Barry Rand, said Ms. Higginbotham-Brooks, a Texas lawyer, had been "unduly alarming." In June, the university's academic deans charged that the institution was plagued with fiscal mismanagement, and sought the dismissal of the chief financial officer. Worries of administrative problems set off a small protest at Howard's convocation last week, with some students carrying signs referring to Ms. Higginbotham-Brooks's letters and the drop in the U.S. News rankings. Dr. Ribeau was not available for comment on Wednesday. But in a statement posted on the university's Web site, he described a "robust renewal strategy" for Howard's academic program, faculty, administration and facilities that was implemented during his term. The university has addressed some of its problems. For the first time in more than three decades, Howard has broken ground on new academic and residential buildings. The three buildings will be finished next year. To address budget problems, the university cut 75 staff positions earlier this year. Enrollment, which had dropped sharply last year - perhaps because of tighter criteria for federal Parent Plus loans - rebounded this year, with tuition frozen at last year's level. Kerry-Ann Hamilton, a university spokeswoman, said that Howard had 1,596 freshmen this fall, its second-largest class in 15 years, and a total of 10,340 undergraduates, up from 9,460 last spring. And under Dr. Ribeau, Howard has increased its investment in the science, technology, engineering and math fields. Many faculty members seem unperturbed by the prospect of the president's departure. "He's an agreeable person, but not seen as totally in control," said Lorenzo Morris, the political science professor who leads the faculty senate. Going forward, he said, Howard needs leadership and stability. Six of the 13 deans at Howard's different schools are serving on an interim basis. Despite its distinguished history, Howard, like other historically black institutions, has had growing difficulty attracting top black students, as elite universities nationwide have stepped up their recruiting in that same pool. Howard accepted more than half its applicants this year, and its students" average SAT scores were substantially lower than those at more selective colleges. While more than 90 percent of Howard's undergraduates are black, at the graduate level, about a quarter of the students are of other races. Founded soon after the Civil War, Howard has produced a long string of prominent alumni, including Toni Morrison, Vernon Jordan and Justice Thurgood Marshall of the Supreme Court. Wayne A.I. Frederick, Howard's provost, will serve as the university's interim president.