Tuesday's daring assault on Nicaragua's national palace is a sharp escalation of an offensive launched last fall by guerrillas intent on overthrowing the government of President Anastasio Somoza.

The attack is also the single most spectacular operation in the sporadic 16-year history of the Sandinista Liberation Front, a homegrown guerrilla group named after a Nicaraguan general who died trying to prevent the 1933 ascension to power of Somoza's father, the patriarch of the 45-year-old regime.

While the attack may not signal the beginning of full-fledged revolution, it has already achieved the interim Sandinista goals of putting Somoza visibly on the defensive, and focusing world attention on the Nicaraguan conflict.

Most significantly, it is likely to have at least tacit support from a large percentage of the rapidly growing anti-Somoza movement that in recent months has thrown the guerrillas, business leaders, peasants, intellectuals and students into a shaky alliance. Their only common goal is Somoza's ouster.

For years, the Sandinistas were no more than a bothersome thorn in the side of the Somozas. Small in number and hazy in ideology, they confined their activities primarily to Nicaragua's mountainous northeast, where they were generally ostracized by fearful peasants and successfully kept on the run by Somoza's National Guard.

Their support outside of student groups was almost nonexistent.

Midway in their history, the Sandinistas were riddled with factionalism, and divided into three groups with goals ranging from pure nationalism and the simple removal of Somoza to the installation of a Marxist-Leninist government.

Next to Tuesday's attack, the Sandinistas' most widely publicized operation came in 1974, at a time when the government was confident of their weakness and had become complacent in its ability to control their activities.

The guerrillas broke into a party in an upper-class Managua home from which the then U.S. ambassador, Turner Shelton, had just left. Taking numerous hostages, they eventually exchanged them for a multimillion dollar ransom and a flight to Cuba for them and several formerly jailed compatriots.

An enraged Somoza subsequently declared a state of siege, giving the National Guard special powers and virtually eliminating all political and press opposition.

With its antiguerrilla real inflamed, the National Guard began a series of operations in the northeastern mountains that over a period of years allegedly resulted in the indiscriminate murder and disappearance of hundreds of peasants.

It was not until early 1976, however, that reports of such operations began filtering outside the country and Somoza came under heavy criticism for human rights abuses. While the United States had always considered Somoza a staunch anti-communist ally, the Carter administration began to cool on the relationship and gradually cut U.S. military assistance.

The U.S. pressure grew until Somoza lifted the state of siege last September, gradually liberalized his government, and promised to withdraw himself and his family from power after elections scheduled for 1981.

By last September, however, non-guerrilla opposition to Somoza had begun to spread. Many Nicaraguans place its real beginning in 1972, when an earthquake devastated the country. Substantial sums of international aid flowed into Nicaragua, and much of the funds ended up in Somoza's coffers through his extensive ownership of Nicaraguan ladn and businesses. For the first time, local businessmen said, Somoza blatantly denied them their accustomed cut in the riches.

Last summer, when a near-fatal heart attack put Somoza out of commission for several months, many Nicaraguans who previously had seen no possibility of his removal seriously began to envision a Nicaragua without him.

By the time the long-dormant Sandinistas launched a series of surprise attacks against scattered National Guard garrisons in October, many former opponents applauded them. By that time, the guerrillas, who had set up operations not only in Cuba but also in Costa Rica, Mexico and Honduras - had swelled in number. They included many of the children of the business and education elite whose support Somoza had long counted on.

Smoldering resentment against Somoza exploded in January with the assassination on a Managua street of opposition newspaper editor Pedro Joaquin Chamorro. While the case remains unsolved, and there has been no substantial evidence that Somoza ordered the murder, most Nicaraguans seem to feel he was responsible.

Since the Chamorro assassination, Nicaragua has been torn by a virtual civil war, with the increasingly widespread opposition demanding Somoza's resignation and the president adamantly refusing to leave. Increasingly frustrated, even some of the most pacifist elements of the opposition have begun to look at the Sandinistas - a group that now includes many of their children - as they only answer.