National security affairs adviser John M. Poindexter made a secret two-day trip to Central America this week to assure nations in the region that President Reagan favors additional assistance to anti-Sandinista rebels in Nicaragua, White House officials said yesterday.

Reagan is to make what a White House official called "strong remarks" about Nicaragua in his weekly radio address today. Officials said the president is reviewing plans to provide the rebels with more aid, probably including a request to Congress for military assistance.

"There is a realization that the democratic resistance needs more help," a senior administration official said.

Reagan has repeatedly tried to pry military aid for the counterrevolutionaries, or contras, from Congress. The contras currently are receiving $26 million in "nonlethal aid," which does not include weapons or military equipment, under a compromise with Congress earlier this year.

Officials said the trip by Poindexter, in his first week as national security affairs adviser, was designed to underscore Reagan's commitment to helping the rebels. Poindexter assumed his new duties last week from Robert C. McFarlane, who will formally leave the White House at the end of the month.

White House spokesman Larry Speakes announced yesterday that Poindexter had visited Guatemala, El Salvador, Panama, Costa Rica and Honduras "to review the current situation with U.S. officials in the region and to meet certain Central American leaders on measures being taken to implement the president's policy of advancing the cause of democracy in the region."

Poindexter was accompanied by Elliott Abrams, assistant secretary of State for Latin American affairs.

In an interview Tuesday with the Associated Press, Abrams said the administration favored renewing military aid to the contras but that no final decision will be made until Congress has been consulted. Speakes said yesterday that there also has been no final decision on the amount of aid Reagan will request for the contras in his next budget.

But the emphasis of officials who spoke yesterday under condition of anonymity was that Reagan will try once more to find a way to funnel military aid to the contras. One senior official said the president's "commitment to providing all possible aid to the democratic resistance remains undiminished."

Speakes said Poindexter was told in the nations he visited "of the need to do more to help the democratic opposition in Nicaragua."

"Many local officials have expressed concern to him over the Cuban involvement in combat operations and the spread of terrorism against democratic governments," he added.

According to administration sources, Poindexter received a particularly blunt assessment of the plight of the contras during his stopover in Honduras, where the rebel force is based. Current estimates are that about 5,000 rebels are operating in Nicaragua, with another 6,000 in Honduras.

Poindexter was told that these rebel troops had been frustrated by the strength and strategy of the Popular Sandinista Army, which now numbers 60,000 and has blocked many of the infiltration routes into northern Nicaragua.

Poindexter assured Honduran leaders of Reagan's continuing support for the rebels but pointed out that congressional obstacles to increased aid remain, an administration official said.

One source said that Reagan's radio speech today will be partly in response to the concern of the Central American governments that Poindexter visited, especially Honduras, that the United States might retreat from its commitment to the contras or so reduce its level of aid that they would be unable to continue military operations.

The source said the president will make clear that his policy is unchanged and that he will seek additional aid. Reagan also will point to recent instances where the Sandinistas are alleged to have supported terrorism in the hemisphere, the source said.