William E. Kirwan, who as chancellor of the University System of Maryland over the past dozen years helped oversee the rise of several of the state's public universities to national prominence, will step down from his position as soon as a successor is found, he said Tuesday.

Kirwan, 76, a gregarious leader who maintained good relations with state officials, university presidents, members of the Board of Regents, faculty, business leaders and students, said he hopes to remain active in higher education with work on expanding access for low-income students.

A former president of the University of Maryland, College Park, Kirwan said the state's public college system has made strides in national rankings, in redesigning courses to appeal to tech-savvy students and in narrowing the achievement gap between white and minority students.

But he also was chancellor when Maryland's historically black colleges sued the state over what they said were disparities in funding and duplicated programs. And challenges remain for the 12-university system to boost enrollment and graduation rates.

After a 50-year career in higher education, Kirwan said he wants to spend more time with his family and that it was "hard to come to grips with the reality of Father Time."

"I came to a very difficult decision," Kirwan said in an interview. "I say 'difficult' because I still feel the same energy and passion I've always felt for the University System of Maryland and its agenda. But I have to face a hard fact: I've reached the age where I need to step back and focus on issues of special interest to me while I have all this energy."

Board of Regents Chair James L. Shea said he would soon put together a committee to conduct a national search for Kirwan's successor. Shea said he hopes to find that person by mid-fall.

Shea praised Kirwan for his work in pushing for courses that use online instruction and more discussion time in the classroom, and for bridging gaps in achievement between low-income and minority students and their peers.

He said the board is looking for a successor who will be aggressive in tackling challenges facing public higher education nationwide, including rising costs and stagnant funding.

"I don't think in today's world you can make a 'safe' choice, someone who can just carry on what's come before," Shea said. "It's not as if we're facing a crisis and need to rearrange everything, but we need a bold leader who can take on the challenges in higher education, which will be enormous."

Freeman A. Hrabowski III, president of the University of Maryland, Baltimore County, said he "cannot think of another system head that is more revered than Brit Kirwan."

"He is seen as one of the leading innovators in American higher education," Hrabowski said. "We have completely redesigned courses. I don't think the public understands the depth of the transformation that Brit has led."

Kirwan, whose nickname "Brit" is a play on his middle name, English, started at College Park in 1964 as an assistant professor of mathematics. He worked his way up at the state's flagship university over the next 35 years to associate professor, professor, chief academic officer and, in 1989, president.

He took the job after John B. Slaughter left amid the controversy surrounding the fatal cocaine overdose of Maryland basketball star Len Bias. Investigators said some athletes had not been attending classes and the coach had not addressed the academic failure of students.

Kirwan, who ran the university's day-to-day affairs during the controversy, insisted on holding athletes to higher academic standards, in the face of criticism from legislators and members of the public.

He left College Park in 1998 to become president of Ohio State University, among the largest in the country. But he was pulled back to Maryland four years later with an offer to become chancellor of the university system.

Shortly after Kirwan returned in 2002, the system raised tuition by an average of 35 percent. But as the economy declined, the new chancellor worked with Gov. Martin O'Malley to freeze tuition for four years, and held off the large tuition increases and mass staff layoffs experienced in other states.

"That doesn't happen by accident," said former Gov. Parris N. Glendening, a longtime faculty member at College Park. "Kirwan was able to work with the governor and say, 'We must really do this.'"

In a statement, O'Malley said Kirwan "has been an invaluable and critical partner in our efforts to strengthen and grow our middle class by expanding access to high-quality higher education in Maryland."

Though College Park, Towson University and UMBC raised their academic profiles during Kirwan's tenure, the state's four historically black schools — three of them members of the university system — sued the Maryland Higher Education Commission in 2006 over funding and programs.