Nicaragua brought the sixth nonaligned summit to its feet today with a speech loudly defending "liberation struggles," denouncing historical "U.S. imperialism" and asking for help in consolidating its own revolution.

While delegates in the sleepy summit session woke up to applaud Daniel Ortega, a member of Nicaragua's new government junta and the Sandinista guerrilla directorate, other nonaligned diplomats labored in closed meetings to iron out a heated internal dispute over the seating of two warring Cambodian governments.

For many of the 94 countries and revolutionary group here, that issue represents what has become a bitter fight over how the nonaligned organization has been run in the past, and how current summit host Cuba, which will serve as movement chairman for the next three years, will run it in the future.

Moderate delegations led by Singapore and Yugoslavia are seeking to codify what have been some unwritten movement rules, and change others, to head off what they see as attempts by Cuba-led activists to make the organization more militant and consequently more closely allied with the Soviet Bloc.

Tanzanian President Julius Nyerere, a key African leader, lent his weight to the moderates in a speech Wednesday night when he warned the summit that if the nonaligned movement tips toward Moscow, "it will cease to be an influence on the world and fall apart."

Nyerere's speech, a forthright rejection of the position espoused most forcefully here by Cuba and Vietnam, drew one of the longest rounds of applause heard at the conference.

Vietnamese Prime Minister Pham Van Dong argued the opposite view, charging that "the attempt to return to the movement's initial objectives" of opposing both the Western and Soviet blocs, "is in essence aimed at making the nonaligned movement deviate from its anti-imperialistic objectives."

Vietnam also is involved in the conference's bitter debate over which Cambodian delegation to seat. In his speech, Dong defended the Vietnamese invasion which toppled the Pol Pot government in Phnom Penh in January as a "justice-radiating struggle of self-defense."

When summit preparatory sessions began last week, host Cuba unilaterally barred the ousted Pol Pot government from attending, despite the fact that many delegations maintained there had been no movement decision on the matter.

While the moderates insist they "hold no brief" for the brutal Pol Pot regime, they say they object to the movement's legitimatizing foreign military intervention by accepting its successor.

Cuba now feels it has compromised by agreeing that neither Cambodian delegation should be seated. The moderates want to avoid approval of what amounted to Cuba's strongarm prohibition of entry for the Pol Pot delegation by having the summit go no further than noting that no decision could be reached.

According to one delegate from the moderate group, "bedlam broke out" at a closed meeting of the foreign ministers last night when Cuba circulated a paper -- intended for approved transmission to the heads of state as the sense of the meeting -- saying they had decided "the seat should not be occupied."

Cuban Foreign Minister Isidoro Malmierca, according to several accounts, then asked for opponents of the paper to speak, and 16 countries answered. Following their strongly worded disagreements, Malmierca banged the gavel, announced the Cuban paper approved for transmission and adjourned the meeting.

"This isn't the Comintern," one delegate reportedly yelled out, while others banged their translation earphones on the table and Malmierca calmly left the room.

As one delegate explained his country's moderate views, the presence of the Pol Pot delegate would be "an embarrassment to Vietnam and the Soviet Union . . . an insult and an effective condemnation of intervention. One of their primary concerns here is unseating the Pol Pot delegation."

"The Cubans don't even really care about it," he said, and are just trying to please the Vietnamese and Soviets.

According to sources, Sri Lanka, which sides with the moderates, has asked for a meeting with Cuban President Fidel Castro on the dispute, but has received no reply.

Cuban Vice President Carlos Rafael Rodriguez met this afternoon with moderates Singapore, Malaysia, Indonesia and Sri Lanka -- all of which claim special interest because of geographic proximity to Cambodia -- along with Yugoslavia and India as supposed "honest brokers" between the disputants, but no outcome was reported.

One strong supporter of the Cuban position on Cambodia is Nicaragua, whose speech today compared the Vietnamese-aided Cambodian struggle to its own.

Delivering new member Nicaragua's inaugural address to the organization, Ortega also declared support for the Palestine Liberation Organization, the independence of Spanish Sahara and the "Puerto Rican people's struggle for self-determination and independence" from the United States.

On other issues, Ortega took positions widely held in the Third World. He expressed hope for the SALT treaty and denounced the Camp David accords as a "betrayal" of the Palestinians.

Ortega reserved special criticism for Israel, which sold arms to the Somoza government the Sandinistas overthrew last July.

Tying most of the world's revolutionary struggles to Nicaragua's, Ortega lengthily described "Yankee intervention" in Central America.

Saying his country "wants to invest in tractors and plows instead of weapons" Ortega asked for Third World solidarity in protecting Nicaragua from counterrevolution.

He denounced "reactionary U.S. circles" for blocking aid money to the new Sandinista-led government.