Soviet President Nikolai Podgorny today received what was probably his warmest welcome so far when he arrived here on the last leg of his three-nation tour through southern Africa.

Thousands of Mozambicans turned out for Podgorny's midday arrival at Maputo airport and President Samora Machel gave the Soviet leader a big bearhug on his descent from the presidential jet that brought him from Lusaka, the Zambian capital.

The crowds were far more enthusiastic here than they were in Dares Salaam or than they were reported to have been in Lusaka. At one point, they almost broke through police lines to move closer to the Soviet president as he watched local dance groups performing in his honor at the airport.

It appears likely that his four-day stay here in Maputo, just 17 miles from the border with white-ruled South Africa, will prove to be the climax of his southern African visit. There is intense speculation as to whether Mozambique and the Soviet Union will sign a friendship treaty similar to the one concluded in October between Angola and the Soviets. ets.

President Mache 1, who visited Moscow last May, has been talking about his desire to establish an "exemplary relationship" with the Soviet Union, which he regards as a "natural ally" along with the other socialist countries.

The editorial in today's edition of the government daily Noticias hailed the Soviet Union as the "first liberated zone of humanity" and noted the common principles uniting Mozambique with it. Chief among these, it said, was the principle of international proletarianism and the common struggle against colonialism, neocolonialism and imperialism.

But it also called for cooperation on the basis of equality and noninterference in the internal affairs of either country.

The Soviet Union provided the Mozambican nationalist movement with most of its arms during its 12-year struggle against Portugal, the former colonial ruler here. The leaders of independent Mozambique have not forgotten this assistance and now regard the Soviet Union as a "sure strategic base" for the African struggle against the white regimes in southern Africa and Western "imperialism."

The Noticias editorial also attacked the Western press for what it said was an attempt to "slander and denigrate" Podgorny's trip to southern Africa. Similar attacks were made in the state-controlled press of Tanzania and Zambia during Podgorny's visit to those countries.

President Machel has defined the "exemplary relationship" he wants to establish with the Soviet Union as one of "mutual assistance and cooperation, wherein each of the parties is conscious of the fact that the success of the other party helps in its own progress and strengthening."

Precisely what form this relationship will take in practice may become clearer at the end of Podgorny's visit here.

So far, Soviet economic assistance to Mozambique has been limited to sending about a hundred doctors and technicians, including port harbor pilots, but the Mozambique government is reportedly paying their salaries.

The bulk of Soviet aid here is primarily military. The Soviets are providing arms not only to the Mozambican army but also to the nationalist guerrillas fighting to overthrow the white-minority government in neighboring Rhodesia.

In fact, the Soviet Union now is the main source of arms for the Patriotic Front of Zimbabwe (Rhodesia), led by Joshua Nkomo and Robert Mugabe. Podgorny saw Nkomo in Lusaka and is expected to meet with Mugabe here.

The Soviet leader began his official talks with Machel today. The two are scheduled to resume their discussions Wednesday.

A Soviet press spokesman said the two leaders would discuss international issues such as detente, disarmament and the Middle East in addition to the explosive situation in southern Africa which is regarded as the main topic of their talks. He said that there was "no question" of the Soviet Union asking for base rights in Mozambique or of the two presidents discussing this issue during their three days of talk.

Thursday, Podgorny is scheduled to address a large rally, the only one held for him during his two-week trip here in southern Africa.