Student riots protesting the authoritarian rule of President Park Chung Hee erupted for the fourth straight day today and Park summoned his key aides to an emergency meeting on the unrest Saturday.

Using tear gas, police dispersed roving bands of students who were shooting slogans against Park's government in the southern city of Masan, the scene of an uprising 20 years ago that triggered a successful movement against Park's predecessor, Syngman Rhee.

Masan, where similar disturbances broke out Thursday, was put under a 10 p.m. to 4 a.m. curfew and its two colleges were closed indefinitely. About 12 persons were taken into custody for questioning.

Observers noted that aside from a quickly quashed attempt to organize a rally at a university in Seoul the campaign against Park has not yet had any serious impact here. Seoul is regarded as the most sensitive barometer of South Korean political attitudes.

Today four students tried to get a protest started in Seoul and quickly drew a crowd of 400 students. Riot police, however, broke up the gathering, firing four tear gas shells into the crowd, witnesses said.

Park called both officials of his administration and leaders his ruling Democratic Republican Party to Saturday's emergence meeting. Sources said the government was concerned about the continuing violence in Masan, 175 miles south of Seoul, and in Pusan, the nation's second largest city, where the original disturbances broke out Tuesday.

The protests were triggered, in part, by the expulsion from parliament of opposition leader Kim Young Sam, a native of Pusan, on Oct. 4. They began with what police called a "premeditated riot" Tuesday when students attacked city buildings in Pusan and called for the overthrow of the government.

On Wednesday and Thursday, 3,000 demonstrators converged on government and private offices in Pusan, setting fire to several buildings and police cars in what was described as the most destructive antigovernment demonstration since Park came to power in 1961.

The government blamed the protests on "subversive elements" and imposed martial law in Pusan, a city of 3 million.

At least 40 people were reported arrested. Soldiers standing on the backs of open trucks and carrying M16 rifles with fixed bayonets rode through the heavily populated sections of the city in a silent show of strength.

On the campus of the closed Dong-A University, site of riots that spilled downtown Wednesday night, troops of the Army's elite Special Forces set up their headquarters.

Tanks and armored cars guarded key government buildings in the city, 205 miles southeast of Seoul.

It was at Masan in 1960 that the death of a student protester sparked nationwide riots that toppled the government of Syngman Rhee. The protests stemmed from Rhee's rigging of elections.

A newsman reported from Masan that armored cars with mounted machine guns guarded the police station following the Thursday night riot in which residents joined students demanding restoration of democracy.

Witnesses said students and their supporters stoned police stations, the city hall and a fire station. They burned a police motorcycle, pushed an empty police truck off a bridge and attacked the Masan office of the Democratic Republican Party.

Defense Secretary Harold Brown, in Seoul for an annual U.S. -- South Korean security consultation meeting, reaffirmed U.S. defense commitments for South Korea against the communist North.

A U.S.-South Korean communique issued after the talks said the two countries agreed on coassembly in South Korea of F5E and F5F jets, and officials said about 70 of the planes would be built.

At a news conference before leaving for Tokyo, Brown said the United States would not use its security role in South Korea to influence policies of the Park government.

Despite Brown's public statement, U.S. officials said he carried a letter to Park from President Carter urging the South Korean leader to ease political restraints in his country. The officials gave no details of the message.