President Reagan, in his weekly radio address yesterday, vowed to continue supporting the rebels battling Nicaragua's leftist government. He said the answer to Central America's woes was political and economic freedom -- not Soviet tanks.

Reagan's remarks came one day after his meeting with Mexican President Miguel de la Madrid, who opposes Washington's backing of the rebels. Although the two leaders agreed on the need to help Latin America repay its huge foreign debt, they did not narrow their differences over the turmoil in Central America.

"The answer to Central America's problems is political and economic freedom, not Soviet tanks and ruthless regimes like the communist dictatorship in Nicaragua that wages war against its own people," Reagan said he told de la Madrid.

The president said this was the reason why his administration "will continue to support those fighting for freedom and democracy in Nicaragua."

Reagan noted that he and de la Madrid had expressed their "respective viewpoints" on the Central American issue, and that the Mexican leader had stressed that the conflict had roots in social and economic injustices.

Reagan said he pointed out that the United States was offering $1.2 billion in economic assistance to help the region alleviate poverty.

Overall, Reagan said, U.S.-Mexican relations were good and that the talks were "marked by an air of friendship." He had high praise for the U.S.-Mexican effort to battle the rising tide of illegal drugs flowing across the two nation's borders, but noted that much needs to be done.

In the Democratic response yesterday, Speaker Thomas P. (Tip) O'Neill Jr. (Mass.) said the new year will see House passage of legislation to force America's trading partners to open their markets to U.S. goods.

Unfair trade practices of other nations are crippling vital U.S. industries, O'Neill said, adding, "It is becoming harder and harder to find industries where our country still dominates the world market."

The United States is running an annual trade deficit of $145 billion, he noted. "If policies are left unchanged, it is expected to be just as large in 1986," O'Neill said.

"I predict that in 1986, the House of Representatives will act on legislation that forces our trading partners to open their markets to American goods and that sets tough sanctions on countries that use unfair trade practices to run up exorbitant trade surpluses.