Mario Savio and other leaders of the 1964 Free Speech Movement returned to the University of California campus today to commemorate the 20th anniversary of that historic protest and to urge students of the 1980s to get involved in political issues.

Standing on the steps of Sproul Plaza, where he once crusaded for student political rights from atop a trapped police car, Savio, now 41, told a crowd of students and Free Speech Movement veterans that campus activism is now more important than ever before.

"Behind the celluloid shield of an actor president, we are now confronted with a Cold War America in its last stand," he said.

Protest now should be against U.S. involvement in Central America, Savio said at the noon rally. "Either we succeed in making this issue the Mississippi of this generation or it will become the Vietnam of our generation," he said.

Savio helped launch the Free Speech Movement after spending a summer registering blacks to vote in Mississippi. Out of the public eye for more than 15 years, he recently received a bachelor's degree, graduating with honors in physics from San Francisco State University.

Today's rally, which attracted about 2,000 people, was part of a week-long schedule of events organized by Berkeley's graduate students to honor the Free Speech Movement and its role in setting the stage for subsequent student demonstrations.

The Berkeley protest was an outgrowth of the civil rights movement and erupted after university officials banned political speeches and fund-raising on campus. When several students defied the ban and set up tables in the plaza, police were called in to arrest the demonstrators.

Jack Weinberg, a former graduate student in mathematics, was dragged from his Congress of Racial Equality (CORE) table and placed in a police car that had been driven onto the campus.

Savio, then a junior majoring in philosophy, shouted for students to surround the car and sit down. Hundreds did so, and Weinberg remained in the vehicle for 32 hours until a temporary compromise was reached between the students and university administration.

In December of that year, after the arrest of 800 persons during a sit-in, the university administration adopted regulations permitting student political activity on campus.

Today's crowd gave Weinberg, Jackie Goldberg, another former Free Speech Movement activist, and especially Savio standing ovations. Each said he had stayed politically active and said it is a myth that current students are less involved.

Weinberg, now an unemployed steel worker from the Midwest, attacked the Reagan administration and warned of the dangers of nuclear proliferation.

Goldberg, a sorority member at the time of the protest and now a high school teacher and member of the Los Angeles School Board, said her generation of protesters looked more clean cut but was not different from today's student activists.

"I know you -- you're not going to allow us to return to the McCarthy era," she said to cheers.

Savio wept briefly during the singing of a civil rights song and addressed the crowd with the same eloquence that had propelled him to leadership during the Free Speech Movement.

Savio charged that the Reagan administration is funding the "contras" in Nicaragua with money taken out of the school lunch program. He said the United States will have to become more democratic and less capitalistic to meet the needs of ordinary citizens, then added, "I'm not a Marxist, so I can say that."

Although the Free Speech Movement and subsequent demonstrations gave Berkeley a reputation as a radical institution, restrictions on campus political activity were opposed by a variety of groups, including Goldwater Republicans as well as liberal organizations.

"It's pluralistic now, and it was pluralistic then," according to Berkeley Chancellor Ira M. Heyman. "It was never a hot bed of racialism, and it's not a hot bed of conservatism now."