Following a rash of renewed terrorist firebombing Thursday, the first anniversary of the military coup that ousted former President Isabel Peron, Argentines were comforted today with an assurance by Montonero guerrillas that they will not attempt to sabotage the World Cup soccer finals here next year.

In a communique mailed to the press, the Montoneros declared they share the general public's "passion" for soccer, and will not deny to "millions of Argentine fans the right to see the best soccer in the world."

Soccer rivals politics as an Argentine national pastime, and an attempt to bring them terrorism into the soccer stadium could have meant an abrupt end to whatever popular support the Montoneros have.

Public enthusiasm for the game is such that soccer rivalries often begin on the playing field and end up in fullscale street demonstration.

With elimination games beginning this month between Latin American countries, and more than a year to go before the World Cup finals begins in July 1, 1978, anticipation already is running high in Buenos Aires.

Argentina, of course, hopes substantial profits from the games, which every four year bring together the world's top 20 soccer teams.

But the government also is looking forward to garnering some international publicity that for once has nothing to do with its position on human rights.

The ruling military junta has come under worldwide criticism for its alleged detention and torture of political prisoners.

While that criticism has increased, domestic terrorism has greatly dimished. In recent months the junta has claimed total victory in what it describes as a "civil war" with the Montoneros, an anti-junta terrorist organization that split from the authoritarian Peronist movement in 1974 and went underground two years ago.

In their communique, the Montoneros offered guarantees to soccer "players and technicians, fans, sports delegation and foreign journalists."

Rather than fearing the guerrillas, the communique said, foreign delegations and journalists should fear that the government "intends to take reprisals against those from other countries who know of their crimes."