Black students at the University of Virginia today invoked a technique of the civil rights era and staged a polite but determined sit-in on the grounds of the school, which has been plagued by charges that its administration is indifferent to minority students.

The confrontation between the administration and almost 100 students ended almost like it began--with demands and promises but no resolutions.

"We want to let them know how tired we are," said Sheila Jackson, a student who brought her 8-month-old son Franklin to the march. "You look around and you wonder when are they going to change."

Both sides conceded that some progress had been made in a day that began with a sit-in at the university's Office of Afro-American Affairs and concluded with a march to the marble steps of the Rotunda--the center of Thomas Jefferson's "academical village" set against the backdrop of the Blue Ridge Mountains.

"I tried to be honest with them," said Ernest H. Ern, vice president of student affairs, who met with black student representatives for more than 90 minutes. He later addressed the protesters in a tense give-and-take that he termed "more symbolic than anything else."

The protests have become an annual spring event for black students, who have demanded that the university take immediate steps to increase black enrollment, provide black students with additional scholarships, and more vigorously seek and hire black faculty. The black students also want the university to establish a department of Afro-American studies and allow academic majors in that area and increase money and office space set aside for black student organizations.

The school is under increased pressure by the administration of Gov. Charles S. Robb and the federal courts to find more black students and has announced that it will accept any qualified black students until the opening day of classes next fall. There are 977 black undergraduates at the university, which has a total undergraduate enrollment of 11,104.

Louis Anderson, chairman of the Black Student Alliance, which says it represents all of the school's black undergraduates, said today's protests were intended to "serve notice" to the administration that black students won't tolerate indifference.

"The problems we are having are the same problems black students were having when they came here in 1971," he said from the aging wooden porch of the Luther P. Jackson Black Cultural Center, named for a black educator and historian, which doubles as the Office of Afro-American Affairs.

One of the most controversial grievances of the Black Student Alliance concerns the performance of Paul L. Puryear, a black who was selected last year as dean of the Afro-American Affairs office.

The words on a banner hung by the black students from Puryear's office window demanded that he "give us our money's worth."

Several black students complained that Puryear did not represent their interests and was seldom to be found when they needed him.

Puryear later told a reporter that a small number of students disagree with his methods of problem solving, which include "talking to white people."

Throughout the day, students drifted in and out of the old Jackson House as stereo speakers blared the revolutionary reggae of Bob Marley. "Stand up, stand up. Stand it for your rights!" the music rang out.

Virginia's All-America basketball center Ralph Sampson wandered, with little fanfare, up to the aging two-story brick house to take his place in the protest.

"Yes, I think the students have legitimate concerns," he said, stopping to pick up a placard and join in the scheduled march to the Rotunda.

"I think a lot of their statements are empty," said Victor Millner, a second-year Spanish major from Chatham in the southwest part of the state.

Another white student, Luke Jordan, a government and English major, agreed that the black students had some points to make but said he didn't really care about most of the charges they were explaining over a bullhorn.

"Around here, most people don't care about anything," he said.