SAN SALVADOR, NOV. 21 -- Ruben Zamora, a political leader allied to El Salvador's Marxist-led rebels, today ended seven years of exile and returned home to launch what he called a "great crusade" for democracy in a major test of political freedoms under the government of President Jose Napoleon Duarte.

Zamora, vice president of the Democratic Revolutionary Front (FDR), arrived this evening on a commercial airliner from Mexico and was met at the airport by about 800 chanting supporters.

"We are going to build a democracy where problems are solved through dialogue and discussion and no longer through threats and death squads," he told the crowd in front of the airport. He then took up a Salvadoran flag and kissed it, saying, "This is the only amnesty I accept."

The act symbolized his rejection of a government amnesty and was apparently meant to recall a White House ceremony last month in which Duarte aroused intense leftist criticism by kissing the American flag. The Salvadoran government has said returning exiles such as Zamora are covered by the amnesty whether they like it or not.

The return of Zamora, a former leading member of Duarte's Christian Democratic Party who fled El Salvador in 1980 after his brother was murdered by a death squad, has heightened political tensions here. Rightist leaders said before Zamora's arrival today that he should be barred from entering the country unless he publicly broke with the Farabundo Marti National Liberation Front (FMLN), an organization of five guerrilla groups that have been waging an insurgency for the past eight years.

Zamora and other leaders of the Democratic Revolutionary Front, a coalition of non-Marxist parties, unions and other groups have refused to split formally from the guerrillas, although their return from exile marks a clear divergence from the rebels' goal of achieving victory through armed struggle. The president of the front, Guillermo Ungo, plans to return from exile Monday accompanied by a large international delegation.

"We consider that in El Salvador it is indispensable to develop a political alternative for a negotiated solution to the conflict," Zamora said on the flight home. He said he had decided to return to El Salvador because this alternative could only be developed inside the country.

"There are risks, it's true," he said. "But the life of an opposition politician in El Salvador is always risky."

He added, "We think our return will not call into question the political alliance of the FDR and the FMLN." He said it would be "stupid" to disavow the FMLN, although he acknowledged that there are both points of agreement and differences within the alliance.

In contrast to demonstrations staged by the guerrillas' supporters, the crowd awaiting Zamora's arrival at the airport appeared to be largely middle class, and the slogans were more moderate.

Zamora, who has been living in Mexico and Nicaragua, called on Salvadorans to "put aside petty differences and sectarian thinking." He has said that he plans to meet with leaders of Salvadoran political parties, including those on the far right, and that he will meet with Duarte if invited.

Although there were no incidents at the airport, several recent killings and kidnapings have raised fears that rightist death squads are back in business and upset about the return of leftist leaders. Death squads have been blamed for about 40,000 of the more than 60,000 deaths in El Salvador's eight-year civil war, but killings attributed to them have dropped off in recent years.

One group demanding punishment for returning leftist exiles has been the Republican Nationalist Alliance (Arena) of Roberto D'Aubuisson, who has been linked with death squad activity in the past.

There is also uneasiness within the powerful armed forces over the return of the politicians.

"It is possible they are only coming for political work, but we do not trust them," said one top officer who asked not to be identified. "What we fear is that their return is a Trojan horse for the benefit of the FMLN."Special correspondent Douglas Farah contributed to this report.