Sen. Richard G. Lugar (R-Ind.), reaffirming his support for Nicaraguan rebels, said yesterday the contras must still produce "much more evidence" that they defend democratic principles if they are to win public backing.

In a speech to the National Press Club, which was billed as a major effort to reframe the Central American debate, the chairman of the Senate Foreign Relations Committee criticized liberals and conservatives for failing to assert democratic goals for the region strongly enough.

He said he had recommended to the Reagan administration, after it successfully defended a democratic process in the Philippines, that it set up a similar policy of "free and fair election ideas" for Nicaragua. The administration found the suggestion "interesting, but not especially welcome" and "distracting" from its drive for $100 million in renewed aid for the contras, or counterrevolutionaries, Lugar said.

That request remains stalled, with a House vote expected next week. "The American people and the Central American democracies will not back any Nicaraguan freedom fighters who have any other agenda than a passion for democracy. The contras need to know that," Lugar said.

"I am spelling it out again, today. I want to see much more evidence that the contras can articulate, loudly and clearly, the constitution that they want to cherish and for which they are willing to risk their lives with our assistance," he said.

Lugar reminded conservatives that they were wrong when they "argued only yesterday that a democratic system was a luxury which the government of El Salvador, fighting for its life against communist guerrillas, simply could not afford."

He said his "liberal friends" also are wrong in espousing "a defensive quarantine" of Nicaragua in which its leftist leaders "would be left to stew in their misery" while neighboring countries maintain strong defenses.

"This policy assumes disastrous internal experiences and pressure from Central American neighbors would lead toward Nicaraguan democratization," and that the Soviet bloc "would leave things alone," Lugar said.

There is no evidence that this would happen in the absence of military pressure, Lugar continued.

"Let me underline the obvious. Military assistance to the contras is the essential factor for any reasonable hope of successful peace negotiations," Lugar said.

Only U.S. diplomats, the presidents of Central America's four democracies and contras together can work, he said.

"We should demand of Managua nothing less than we did of Marcos," Lugar said, referring to ousted former Philippine president Ferdinand Marcos.

"This is the kind of policy goal the American people can understand and support."

Lugar, who was instrumental in shaping the administration's successful Philippine election policy, also has led the fashioning of bipartisan Senate and committee compromises on other difficult foreign policy issues, including a foreign aid bill, the extradition of Irish terrorists, security renovations at U.S. facilities abroad and partial economic sanctions against South Africa.