The first national convention of Poland's independent Solidarity trade union federation opened here today with a ringing appeal for unity from its leader, Lech Walesa. The 892 delegates from all over Poland gave him a rousing ovation when he declared that victory was certain as long as the union did not succumb to factional infighting.

The formal opening ceremony coincided with a show of Soviet naval strength in the Baltic Sea, just a few miles from where the delegates were meeting, and Soviet Army exercises along the Polish border.

The Soviet Union announced tonight that nearly 100,000 troops and naval personnel are taking part in the maneuvers. This is four times as many as Western observers had expected to take part in the exercises, which U.S. officials have called "attempted intimidation" by the Soviets.

A Tass news agency report said the operation was simulating combat conditions to the maximum possible degree, Reuter reported from Moscow. The Soviet Union has insisted that the exercises, directed by Defense Minister Dmitri Ustinov, will be limited in scope, and it has criticized Western suggestions that they are intended to put pressure on Poland.

The Solidarity convention, the climax of a three-month election campaign among the union's 9.5 million rank-and-file members, is being held in a modernistic sports hall on the outskirts of Gdansk -- the port city where Solidarity was born just over a year ago.

By stressing the need for discipline and unity, Walesa was echoing a theme from August last year when he led the strike at the Lenin Shipyard here. What began as a relatively minor incident eventually mushroomed into a huge, and so far politically unstoppable, social movement, as workers throughout Poland joined in a protest against 36 years of communist rule.

Walesa said: "If we remain united, as we were in August, then we will be able to build Poland and make it the Poland of our dreams."

Walesa's speech and the rapturous applause masked for a moment Poland's grave economic and political crisis. After a year of labor upheavals, it is still unclear whether an independent union such as Solidarity is compatible with a one-party communist state.

By putting such a strong accent on unity, Walesa could be attempting to strengthen support for his policy of gradual change and compromise with the government. Over the last few weeks, several local Solidarity chapters have conducted wildcat strikes without the approval of the union's national leadership.

Walesa and other Solidarity officials have described the convention as a crossroads for the union federation, which must decide whether it wants to become a wide-ranging political movement dedicated to Poland's transformation or a trade union pure and simple.

The continuing power struggle with the communist authorities was reflected in the union's decision to refuse press accreditation to state radio and television on the ground that it could not count on objective coverage. Solidarity officials had demanded some form of editorial control over programs devoted to the congress -- but this was rejected by the authorities.

Walesa drew prolonged applause when he accused the government of masterminding an antiunion propaganda campaign. He added: "They must finally understand that Solidarity is a fact and will remain one, whether they like it or not."

Journalists for state radio and television said they would attempt to cover the congress as best they could. This will probably mean reporting the highlights of the meeting in news programs but dropping plans to broadcast extended excerpts from the debates.

From Solidarity's point of view, it is more important to secure adequate coverage of the second stage of the meeting, which will be held at the end of the month. At that session the union's program will be debated in detail and a leadership elected.

The present stage, which is scheduled to last until Monday, will be devoted largely to procedural and internal organizational matters.

Despite the new strains in relations with the communist authorities, a government delegation is attending the convention and was greeted by Walesa. It is led by the minister for trade unions, Stanislaw Ciosek, who made a speech calling for Solidarity's support in overcoming Poland's crisis.

Ciosek said the country needed peace and work rather than continuous conflict. Anyone opposing the country's legal and political system, he said, seriously imperiled its very existence.

Solidarity officials said the Communist Party-dominated trade unions of Poland's Soviet Bloc neighbors had been invited to send observers for the congress, but had not acknowledged the invitation. Yugoslavia, which pursues an independent foreign policy and has shown considerable sympathy for the Polish workers, was the only communist country to send a delegation.

Western countries, including the United States, were represented by low-level delegations.

Before the opening of the meeting, about 5,000 Solidarity members crowded into the local cathedral to hear mass conducted by the new Roman Catholic primate, Archbishop Jozef Glemp. Solidarity, he said, had been born out of anger, but must now work to bring peace and order to Poland.

In Moscow, a Tass news service dispatch on the military maneuvers said, "The operational staffs, units and elements with a total strength of nearly 100,000, which are to participate in the maneuvers, have taken pre-set staging areas and positions," United Press International reported.

The forces have been carefully trained "and are determined to act efficiently," Tass said. "The personnel view the exercises as a test of their combat maturity."

The war games pit a hypothetical northern army based in the Soviet republics of Estonia, Lithuania and Latvia against a southern force in the Byelorussia military district, Tass said, according to UPI.

The Tass report came a day after the United States said the Kremlin had failed to inform the West fully about the maneuvers in violation of the spirit and letter of the 1975 Helsinki accords. The accords' so-called "confidence-building measures" require notification by signatories staging war games if more than 25,000 troops participate, UPI said.