SAN FRANCISCO — A salary agreement that forestalled an unprecedented faculty strike at the California State University's 23 campuses would increase salaries by 10.5 percent over three years and double how long it takes newly hired instructors to be eligible for retirement benefits, university and union officials said Friday.

The tentative deal between the 26,000 member California Faculty Association and the nation's largest public university system represents a compromise and comes as both sides girded for an unprecedented five-day work stoppage.

Union members and the university's governing board still most approve the contract, which would cost about $200 million and require additional state funding to implement, Chancellor Timothy White said in an interview with The Associated Press.

"This dispute was an unfortunate symptom of a core problem in California, which is that the California State University and for that matter, the University of California are underfunded relative to the state's need for an educated populace," White said.

The faculty association, which represents professors, lecturers, librarians, counselors and coaches, had scheduled a systemwide strike starting Wednesday to protest the size of the pay increases the university planned to give its members this year.

Union members currently are in the second-year of a three-year contract that included across-the-board pay raises of 3 percent for the 2014-15 school year. Under that contract, salaries for subsequent years had to be renegotiated.

Before the agreement was reached, the union had demanded a 5 percent increase for 2015-16. The university had said it could only afford 2 percent.

The framework hammered out by negotiators for the two sides would meet the union's demand for an across-the-board 5 percent raise on June 30, White said. The next day, which marks the start of a new fiscal year in California, faculty salaries would be increased by the 2 percent the university had offered for the current year.

During the last year of the contract, all union members would receive another 3.5 percent salary increase, and about half would qualify for an additional 2.7 percent bump tied to their years of service, according to White.

"The breakthrough was to reach agreement on trying to solve the problem over three years instead of over three months. That gave us the breathing room we needed," he said.

The average salary for full-time faculty at CSU campuses varies by academic rank, with full professors earning an average of $96,660 as of last fall, assistant professors earning an average of $73,888 and lecturers making $58,265, according to the university.

An independent fact-finding panel assembled after negotiators reached an impasse sided with the union, however. The panel issued a report late last month stating that boosting faculty pay by the requested amount was "in the interest of students, who need caring faculty."

While the agreement represents a victory mostly for the union, the system extracted a cost-cutting concession with a change in the number of years faculty members must work before they become vested in the university's retirement plan. Currently, new employees must work five years to qualify for retirement benefits. The proposed contract would increase that to 10 years for faculty members hired after Fall 2017, White said.

CSU is the nation's largest public university system, with about 460,000 students. It has not been subject to a full faculty strike since system-wide collective bargaining began in the early 1980s.