Despite widespread arrests of opposition leaders and youthful protestors, the nationwide general strke to overthrow Nicaraguan President Anastasio Somoza appeared to be holding firm yesterday.

In the modern shopping centers around Managua, all but a few stores were closed. The exceptions appeared to be businesses owned by the Somoza family or with connections to officers of the National Guard, Nicaragua's combined armed forces and police.

Explosions punctuated the night-time hours as they have for the past week. They were thought to be homemade bombs thrown by opponents of the government in poor neighborhoods around the city. Stores and factories that remained open have also been hit by the homemade explosives.

Somoza has said the opposition is communist-inspired and he has vowed to remain in office. The government responded to the opposition movement yesterday with renewed pressures on businessmen participating in the strike and a wave of arrests.

Roberto Veles, a leader of the opposition Conservative Party, estimated that 60 high -ranking political leaders and about 600 other people have been arrested in the past three days.

Representatives of three major opposition groups have said that this week will be crucial in the effort to overthrow Somoza, whose family has ruled Nicaragua with the backing of the National Guard for 44 years.

Two news conference yesterday morning were interrupted by telephone calls announcing that Somoza opponents had been arrested.

At the office of the Nicaraguan Development Institute, an organization of 700 businessmen, reporters were leaving when the group's executive director William Baez called out, "Please come back, we have an announcement to make.

"Our vice president, Jose Francisco Teran, was arrested at 9:00 this morning when he was on his way to this press conference." Baez, perspiring under the television lights, paused and added: "If this continues any one of us can be taken to prison."

Later, at the headquarters of the Conservative Party, the only legal opposition group, a telephone call interrupted a reporter's question. A party leader who answered the phone announced that a lower-level Conservative leader had been arrested, as had Noel Rivas, a vice president of the Chamber of Commerce.

All political parties except Somoza's, as well as the Catholic Church and the major business, labor and professional organizations have united to demand the resignation of Somoza.

The arrests during the weekend and yesterday were so widespread that some Conservative Party leaders appeared to be embarrassed that they had not been arrested. They explained that most of them are members of the virtially powerless Congress and therefore have immunity from arrest.

"Somoza does not want the Conservative Party to have the glory of having its leaders in prison," one said. Another added: "We will be the last to be arrested."

One Conservative Party alternate deputy was detained briefly in the town of Chinandega, a party leader said. He was released as soon as his captors learned of his status.

Despite its name, the Conservative Party backs social and economic reform and has joined the anti-Somoza front, which also includes leftist groups.

The president of the Nicaraguan Development Institute, Manuel Jose Torres, said the strike appeared to be at least 80 percent effective among stores in Managua and that many factories were also closed.

He said businessmen who supported the strike were making preparations for it to last one to three months. Many of the shopowners who support the strike pay their employees half salaries.

The government has stripped the organizations supporting the strike of their charters and has asked the banks to provide a list of all stores supporting the strike that have loans outstanding. The banks have been ordered to take action against striking debtors, Baez said.

Whether the banks will cooperate with Somoza or the strikers is still unknown.

Asked why most banks are still open, Torres said they are subject to more pressure from the government than other institutions.

He said that every day the banks remained open depositors were withdrawing more money.

Central Bank President Roberto Incer reported late last week that between $20 million and $30 million had been withdrawn from Nicaraguan banks in the previous two weeks.

Another area where the strike visibly was not effective was transportation. Buses and taxis were running and many gas stations were open. One Nicaraguan businessman said the bus companies are owned by National Guard officers while other officers control the issuance of taxi licenses.

At the Centro Commercial Managua, a large shopping center on the south side of the capital, all but a few stores were closed and there were no shoppers to be seen. A handful of National Guard troops, armed with American-made pistols and sub-machine guns, stood guard.

In a lingerie store, a clerk said the company had decided to remain open because the government had audited its books after it participated in a similar strike earlier this year. She said the clerks had reported to work because the store owner could replace them easily.

The owner of a hardware company said his competitor, a company owned by Somoza, had wanted to remain open. The employes, however, told the company that they would burn the store if it opened.