President Anastasio Somoza met with his Cabinet and members of his Liberal Party today to tell them of his decision to resign, but assured them that among the conditions for his departure are the preservation of the party and safeguards for them and their families.

Somoza said he was determined to negotiate assurances that the National Guard would remain intact.

Meanwhile , in an apparent attempt to improve its bargaining position before a new government, the National Guard stepped up attacks against Sandinista guerrillas.

In the southern cities of Masaya and Rivas, the Guard reported advances against the rebels. Radio Sandino, the guerrilla station, accused the Guard of using napalm, but there was no confirmation of the charges.

Despite the new surge of National Guard action, the Sandinistas appear assured of an eventual military victory. But political negotiations over a future government to replace Somoza have been slowed by faulty communications, widespread misunderstandings and little apparent inclination by the rebels to compromise.

There is general acceptance by most parties, including Sandinista guerrillas, moderate Nicaraguan opposition groups, Somoza and the United States, that the new government will be centered on a provisional civilian junta appointed by the Sandinistas.

The remaining questions revolve around whether the composition of the current five-member junta will be changed, and the agreements it is willing to enter into before assuming power.

In an interview Friday, Somoza acknowledged that he had agreed to resign, but he left the timing for his departure to the United States, which is proposing that moderates be added to the junta membership.

Those wanting to change the composition of the junta have a sense of urgency in the face of possibly imminent Sandinista military victory.

According to diplomatic sources, U.S. concern is only that the new government be "viable."

"The problems are going to be severe for any government here," one source said. After nearly six weeks of civil war, public order in Nicaragua has been replaced by widespread anarchy.

The National Guard - a combined police and army - devotes its time to fighting the Sandinistas, while guntoting bandits, claiming to be guerrillas, move quickly into urban areas as combatants move out. War damage and looting have destroyed nearly all of Nicaragua's businesses and industries.

The United States believes that any new government will need money and authority both of which it feels are chancy commodities for the existing junta.

Without a moderate, stable government, the United States feels, the new government will not attract aid and credit from the West. Without money, it will be unable to satisfy the demands of hundreds of thousands of unemployed and underfed Nicaraguans and the anarchy will continue.

At the same time, the United States believes a weak government will not be able to disarm and control more radical Sandinista factions and that a government not adequately representing moderate business and political groups will not be able to count on their support.

The junta believes, however, that these concerns are part of the U.S. desire to run things in Nicaragua and an expression of U.S. rather than Nicaraguan, worries.

Junta members contend that they adequately represent all opposition sectors. The five junta members comprise two from the Broad Opposition Front, a coalition of seven political organizations, one Sandinista and two representing leftist and left-center groups allied to th guerrillas.

The Broad Opposition Front and Nicaragua's Superior Council of Private Enterprise, representing the nation's business groups, have their own image problems because of the long U.S. involvement in Nicaragua and their association with Somoza.

Anxious not to be viewed as U.S. pawns, they have publicly supported the junta.

The United States says the moderates have privately expressed concerns similar to its own. The junta says it has had no complaints from the moderates. Even by combining its public and private statements, it is difficult to determine exactly how the moderate opposition feels.

One of the biggest problems is that the junta is in Costa Rica and the moderate groups are here. What little communication is possible comes through Nicaragua's increasingly sporadic and government-bugged telephone system or is funneled through a half dozen intermediaries - including Nicaraguan exiles in places such as Venezuela and Miami. CAPTION: Picture, A child helps push a cart carrying family belongings from Jinotepe, where rebels battled Somoza's troops. UPI