In apparent sympathy with the South Korean students who are barricaded in the U.S. Information Service building, about 7,000 university students here staged campus demonstrations today, chanting antigovernment slogans as U.S. Embassy officials tried to settle the sit-in with several dozen students inside the building.

Hundreds of demonstrators on one campus threw rocks and gasoline-filled bottles, and police fired tear gas in return. There were similar student demonstrations on four other university campuses, news agencies reported.

A U.S. Embassy spokesman said the embassy would continue its efforts for a peaceful end to the sit-in. The spokesman said the students asked for bottled water and salt, which the embassy supplied.

Embassy officials said that there were at least four meetings between U.S. officials and the students today but that the negotiations had failed to resolve the situation.

U.S. Ambassador Richard Walker sent a letter to the students saying he could not support the students' violent methods and urging them to leave the building with "quiet dignity."

"At an appropriate moment, after you have returned to your homes and campuses, I shall be happy to meet with a representative group from among your number," Walker's letter said.

The South Korean university students occupied the library on the second floor of the four-story USIS building yesterday, denouncing their government and demanding a U.S. apology for its alleged role in the Kwangju uprising, which began May 18, 1980, one day after the South Korean military issued an order extending martial law and cracking down on leading opposition figures. It went on nine days before a full infantry division and a brigade of paratroopers put down the resistance by force.

By official government figures, 191 persons died in the clash, but human rights groups and dissident leaders contend that the toll was much higher.

The Kwangju issue has been one of the most sensitive facing the government of Chun Doo Hwan, and the newly emerging opposition New Korea Democratic Party has made a new investigation of the incident one of its major demands in the current session of the National Assembly.

U.S. officials have denied responsibility for the deaths at Kwangju, but dissident and student leaders have said the U.S. military, which has maintained operational control of the South Korean armed forces, approved the mobilization of troops for what they call the "Kwangju massacre."

Some political observers expressed fear that the continuing sit-in may spread anti-American sentiments among South Korean student groups.

The latest estimate of the number of students in the library is 73, from five major Seoul universities: Korea, Yonsei, Sungkyunkwan, Sogang and Seoul National.

Several hundred police were standing by, but they will not enter the building unless it is requested by embassy officials.

Embassy officials said their policy is not to ask for intervention by the Korean police while they try to settle the matter through dialogue.

In a hearing at the National Assembly, Prime Minister Lho Shin Yong called the students' actions "outrageous and illegal" and said the government would deal with the students sternly. Lho met for 30 minutes with Walker this morning.

The best known opposition leaders, Kim Dae Jung and Kim Young Sam, sent Shin Ki Ha, a national assemblyman from Kwangju, to the scene to urge the students to meet with South Korean and U.S. officials. However, the embassy has been reluctant to accept intervention by political figures.