Vietnamese Prime Minister Pham Van Dong returned from Moscow today declaring himself "completely satisfied" with a series of agreements made there and pledging full efforts to carry them out.

In a brief ceremony before the assembled Politburo and government ministers and with reporters also present, Dong called the highest level Soviet meetings since November 1978 "an important event at a most important time."

The previous Moscow meeting, at which Vietnam signed a friendship pact with the Soviets, preceded the Vietnamese invasion of Cambodia by only one month. But there were no clues in Dong's remarks here or in Hanoi press reports from Moscow suggesting any special political or military significance to the just-concluded meeting.

The two governments in a joint communique issued in Moscow charged that "Peking, with the support of America, is now seeking to cause instability in Southeast Asia with the aim of putting up a military show of force along the Sino-Soviet border."

The communique also charged that "recent complications" along the Thai-Cambodia border have "direct links to Peking's policy of expansionism." tChina last week warned Vietnam that it faced grave danger if it continued its military raids against Khmer Rouge guerrillas based in Thailand.

In a brief address, Dong referred to an agreement signed in Moscow for joint Soviet-Vietnamese oil and gas exploration along the continental shelf near southern Vietnam.

That agreement may help to explain letters Vietnam recently sent to American firms that have been exploring for possible oil and gas deposits in the South China Sea warning of dangers in view of disputed claims there. Several European countries also have been prospecting in the area.

Also believed discussed in Moscow was Vietnam's need for more than 2 million tons of rice to make up for its shortfall and to feed its people. Due to a poor rice crop, the bulk may have to come from the Soviets.

As he entered the red-carpeted hall, Dong clasped his hands in a victory gesture similar to a prizefighter's while some famous names from the Vietnam war years looked on. They included Defense Minister Dung Van Tien, commander of the final campaign against Saigon in 1975, and former National Liberation Front chief Nguyen Hu Tho, now acting president.