President Reagan told ambassadors of member nations of the Organization of American States yesterday that although the Caribbean Basin initiative appears to have died this year, it remains key to his policy for the area and will be among the first pieces of legislation he submits to the 98th Congress.

Speaking to the group at the White House, the president said a majority of senators supported the bill but that it failed because of "procedural maneuvering by a small minority of opponents." Reagan portrayed the bill as an American gesture in support of Central American democracies and their economies. He said the United States and the entire hemisphere face "threats of insurgencies supported by Cuba and other Soviet satellites." Reagan had outlined the proposal to the OAS last February as a remedy for its economic problems.

"But what I want you to know," he told the ambassadors, "is that the Caribbean Basin initiative will not die."

Later he added: "The time is short, the needs are great, but we will win this fight because there is no acceptable alternative. Together, we are a tremendous force for good. We will show the world that we conquer fear with faith, that we overcome poverty through growth, and that we counter violence with opportunity and freedom."

Reagan said the initiative, which would allow 28 countries to export goods to the United States duty-free, is essential because free trade will prevent the economic problems that unsettle the governments of those countries. Unemployment in those countries now ranges between 14 percent and 40 percent.

In addition to the free-trade provisions, the initiative also includes $350 million in direct economic aid. That part of the administration proposal has already been approved by Congress.

Reagan also told the ambassadors that the United States has agreed to major elements of a plan to replenish the Inter-American Development Bank, including a lending program, supported by several countries, of $13 billion.

White House spokesman Larry Speakes blamed the failure of the initiative on lobbying by organized labor. When the initiative passed the House last week, AFL-CIO President Lane Kirkland said it would result in fewer jobs for Americans.

The administration countered that less than 4 percent of total U.S. imports come from the area.

Meanwhile, the White House announced that Reagan will sign an executive order today giving the bipartisan commission looking for a solution to the financial problems of the Social Security system an additional 15 days to issue its final report. The group had asked for a 30-day extension of its Dec. 31 deadline.