The prime minister of Vietnam, the foreign minister of Cuba and the deputy foreign minister of the Soviet Union all arrived here today for talks with the Indian government.

Government officials called it a coincidence. But Eastern bloc, Western and Asian diplomats speculated it signaled a Moscow-backed attempt to gain wider support for the Soviet Union's three-month-old invasion of Afghanistan. India not only plays a prominent role in regional affairs, but also is influential within the non-aligned movement.

"There is definitely something in the air," said an East European ambassador here.

A spokesman for the Indian government denied that the Communist-bloc officials had come here to put pressure on Prime Minister Indira Gandhi to swing further behind the Soviet action in Afghanistan.

"She is not subject to any influence," the spokesman said, repeating Gandhi's statement that she is neither pro-U.S. or pro-Soviet, but rather, pro-Indian.

The only visitor to meet with Gandhi was Vietnamese Prime Minister Pham Van Dong, who spend 75 minutes in private talks with the Indian leader. He is scheduled to spend six days visiting India.

Cuban Foreign Minister Isidoro Malemierca arrived here this afternoon from Kabul, following a visit to Moscow, and carrying a letter from Cuban President Fidel Castro to gandhi which he will deliver Tuesday.

According to well-placed Indian sources, the Gandhi government would have preferred that Malemierca stay way, but could not refuse his request for talks here.

According to reports circulating here, the Indians disagree with a Cuban plan -- presented by Malemierca last month in Kabul and Pakistan -- to settle the Afghan situation through private talks between Afghanistan, Pakistan and the Soviet Union rather than by using the nonaligned movement.

The Cuban initiative, believed by Western diplomats here to be a Moscow-inspired effort to gain support from the nonaligned and Moslem nations, was rebuffed by Pakistan President Mohammed Zia ul-Haq, who said Pakistan would have no contact with Afghanistan while Soviet troops occupied that country.

Deputy Soviet Foreign Minister N. P. Firyubin will see Foreign Ministry officials, but both Gandhi and Foreign Minister P. V. Narasimha Rao were said to be tied up tonight.

The Soviet diplomat came here from Katmandu, where attempts to gain support for Moscow's invasion of Afghanistan were rebuffed by Nepalese officials.

Although Firyubin walked away when reporters asked if Afghanistan had been discussed, Foreign Minister K. B. Shahi said he had repeated Nepal's demand for an immediate withdrawal of Soviet troops from Afghanistan.