Some 3,000 Yale University workers went on strike Wednesday morning, hoping to extract higher wages, more job security, and fatter pensions from the Ivy League institution. The employees have been without a contract since January 2002.

The strikers -- clerical, technical, service, and maintenance employees -- formed picket lines on the campus, in New Haven, Conn., slowing the progress of graduate students who were returning for the fall semester. Undergraduates are to arrive Friday, and classes will begin next week.

University officials sought to minimize the strike's impact on campus activities, saying managers and temporary workers would pick up the slack. Dining halls, for example, will remain open for freshmen, but upperclassmen will be given vouchers for meals at local restaurants.

Before the strike, a group of eight retired university workers gathered in a conference room in Yale's investment offices on Tuesday evening and refused to leave unless they were allowed to meet with David F. Swensen, Yale's chief investment officer. The sit-in was intended to focus attention on pensions that the protesters said are too low.

Joining the protesters was the Rev. Jesse Jackson, the civil-rights activist, who brought food to the pensioners. Afterward, he said that the plight of Yale's current and former workers is "a metaphor for workers all around the nation." On Wednesday afternoon, the pensioners were granted a meeting with Mr. Swensen, who manages Yale's $11-billion endowment.

Yale's president, Richard C. Levin, characterized the union's demands as "unrealistically high." In a letter to students and members of the faculty and staff, he outlined Yale's contract offer, including annual salary increases of 3 to 5 percent. Mr. Levin said that Yale's defined-benefit pension plan, together with Social Security benefits, would provide employees who retired with 30 years of service, at age 65 or older, with after-tax income of 83 percent to 93 percent of their final after-tax salaries.

Yale also is offering $1,500 signing bonuses to workers who have been employed since before the last labor contract expired. Other workers would get $500 each.

Union leaders said Yale's offer isn't good enough. Clerical workers at Harvard University are paid 57 percent more than workers holding similar positions at Yale, the union said. (The cost of living in Cambridge or Boston, however, is higher than in New Haven.) Under the pension plan, a Yale worker with 20 years of service could retire with a pension of just $700 per month, according to statistics on the union's Web site.

"When I retire, I will retire into poverty after 30 years of service," said an unidentified Yale worker who appeared on a news broadcast by WTNH, a New Haven television station.

Workers walked off their jobs on Wednesday, despite last-minute efforts by New Haven's mayor, John DeStefano Jr., to avert a strike. According to the union, Yale is the city's biggest employer, with one of every four of the city's residents working for the university.

Labor stoppages are not unusual at Yale, which has a history of poor labor relations with its faculty and graduate students as well. During the past three decades, strikes have become a routine part of contract negotiations. The employees on strike now, members of Locals 34 and 45 of the Hotel Employees and Restaurant Employees International Union, also struck earlier this year.