A large government-sponsored rally Sunday to support beleaguered Nicaraguan President Anastasio Somoza triggered renewed anti-Somoza protests yesterday in which at least 10 persons were killed.

The protests broke out after Somoza appeared before a large friendly crowd in Managua and said he would continue to rule Nicaragua until his term ends in 1981.

In his speech, delivered from a bulletproof glass booth in a city plaza, Somoza pledged to allow all political parties to take part in future elections and to name a committee of leading citizens to investigate the assassination last month of newspaper pulbisher Pedro Joaquin Chamorro.

The Nicaraguan government had predicted that more than 200,000 people would turn out to hear Somoza's speech, his first since Chamorro's assassination set off a general strike and a rash of protest across the country.

News services reported that between 80,000 and 100,000 persons actually attended, and other sources put the number below 50,000.

Sources at La Prensa, Chamorro's newspaper, said in a telephone interview that the government had gone to extraordinary lengths to organize the Pro-Somoza rally, pressuring government employees to attend and sending government vehicles into the countryside to bring demonstrators to Managua.

One of the antigovernment protests began, these sources said, when buses and cars that carried demonstrators to the Managua rally were attacked by opponents of the government in Diriamba, 37 miles south of the capital.

News services reported that National Guard troops fought demonstrators for several hours in Dirimba, killing seven persons and wounding 15. The National Guard said the casualties were members of the leftist Sandinista National Liberation Front, but sources at La Prensa said they were ordinary residents of the town.

Another clash was reported at Masaya, 21 miles southeast of Managua, where the National Guard - Nicaragua's combined police and army - said 13 persons were wounded. The Red Cross said 10 persons, including one soldier, were killed throughtout the country. Other sources put the number higher.

Associated Press said hundreds of persons were reported arrested during the antigovernment protests.

The protest have continued off and on since Chamorro was assassinated Jan. 10. The newspaper publisher was a longtime enemy of the Somoza family, which has controlled Nicaragua for 40 years. His Conservative Party is the only opposition party permitted to function in Nicaragua.

Somoza's opponents have accused the government of failing to investigate Chamorro's murder thoroughly.

Chamorro's widow reiterated accusations that Somoza was responsible for the killing at a meeting yesterday in Cancun, Mexico of the Inter-American Press Association.

Violeta Chamorro told newspaper publishers from Latin America and the United States that "no one, in Micaragua or the rest of the world, doubts that my husband was assassinated because of his campaign against the regime of Anastasio Somaza."

She said the government had been harassing La Prensa and Managua radio stations by cutting off electricity and telephones.

Somoza, who was educated at West Point, is a longtime ally of the United States. Relations between the two countries became strained last year, when the State Department and members of Congress criticized the Nicaraguan government for violating the rights of peasants and opposition figures.

Economic aid to Nicaragua has been cut off, but Somoza's supporters in Congress salvaged military aid to the National Guard.

In his speech Sunday, Somoza repeated earlier pledges that he would not seek re-election after his term ends in 1981, and added that he would retire as head of the National Guard at the same time.