President Reagan, on the threshold of a new campaign for aid to the Nicaraguan rebels, said yesterday that public support for the contras has grown "dramatically" and "the American people are tired of the on-again, off-again policy in Central America."

Reagan did not directly mention the Iran-contra scandal and the congressional hearings, which have included impassioned appeals for the rebels by Lt. Col. Oliver L. North and others. Polls reported in the past week suggest that those appeals have increased public support for more aid.

"Now some tell me that the people in this country just don't care about the freedom fighters. But I don't think that's true," Reagan said in his weekly radio address from Camp David. "The more people know about the Sandinista communists, the more they support the freedom fighters.

"A bipartisan majority supported aid to the freedom fighters last year. The American people want that aid to continue, and that's why we've got to get the message out. Talk to your family, your friends, your neighbors, even your congressman and senators," he said.

Reagan's speech came as White House and State Department officials are working out details of Reagan's request to Congress for contra aid for the year beginning Oct. 1. Presidential spokesman Marlin Fitzwater has said the request may be in the range of $130 million, but others suggest the amount could be higher. The rebels were voted $100 million for this year after a protracted battle in Congress, but the Iran-contra scandal has led many lawmakers to question whether Reagan can win approval of aid for another year.

The White House has expanded its team working on the contra aid issue by hiring former representative Tom Loeffler (R-Tex.) to assist with congressional strategy and lobbying, and former State Department public diplomacy specialist Chris Arcos to work on communications efforts.

Reagan's appeal yesterday followed new public opinion surveys showing that the testimony of fired National Security Council aide North and former national security adviser John M. Poindexter may have led to a surge, at least for now, in support for the rebels.

Throughout Reagan's presidency, a wide majority of Americans have consistently expressed opposition to military aid to the contras. However, in the most recent Washington Post-ABC News poll, taken last Wednesday night, two of five questioned said they favor granting military aid to the contras. In June, only 29 percent approved military aid.

Differences in the way the polls were conducted make comparisons risky, but other surveys have also recorded a similar shift in public sentiment. For example, in a Los Angeles Times poll last week, respondents were evenly divided on aid to the contras, compared to a 54 percent opposed, 31 percent in favor finding in February. White House polls also show increased support. A New York Times-CBS News survey published yesterday also recorded a shift in sentiment, but not as great, toward aiding the rebels.

Reagan reiterated yesterday his criticism of the Sandinistas, citing the "apparatus of a police state" without freedoms of speech, religion and assembly. After the regime took power eight years ago, he said, "The ranks of political prisoners swelled into the thousands, and beatings, tortures and official murder became the order of the day."

He added, "If the Sandinistas get their way, the torment of that sad country will soon spread throughout the entire region, engulfing the young democracies that surround Nicaragua."

The president said the Sandinistas "will never negotiate seriously unless they see the freedom fighters are a force to be reckoned with. Without the freedom fighters backing them up, negotiations can amount to no more than a hoax."

Critics of contra aid have claimed that the Reagan administration never intended to sign a treaty with the Sandinistas. In a 1984 document made public by the Iran-contra panels, Poindexter said the United States could continue to negotiate with the Sandinistas but should not sign a treaty. Poindexter said in testimony that the comment represented his personal view that the Sandinistas could not be trusted to abide by a treaty, and that this was not official administration policy.

Yesterday, Reagan said the Soviets have spent "over $1 billion to prop up the Sandinista regime" and added, "The Soviets know what's at stake in Nicaragua, and they know that the freedom fighters are all that stand between them and domination of the entire region."