President Reagan is planning a trip next month to Grenada, the site of the October 1983 U.S. military invasion that toppled a Marxist government, administration sources said yesterday.

The surprise visit is intended to showcase the economic strides that the impoverished Caribbean nation has made since the U.S. military action made it possible for a return to democratic government, the sources said.

The president is tentatively scheduled to visit the island for six hours on Feb. 20, although the officials said the plans might be altered to include a one-night stay.

Because the United States is held in high esteem in Grenada for the rescue mission, officials involved in planning the visit said they expect a large turnout from among the island's population of 110,000.

The mission rescued more than 600 American students at the island's St. George's University school of medicine.

A White House spokesman said he could not comment on the president's future travel plans.

During the visit, Reagan is scheduled to dedicate the new airport at Point Salines and lay a wreath at a monument in the capital of St. George's dedicated to the 19 U.S. military personnel who were killed in the fighting. He also plans to meet with Prime Minister Herbert Blaize and with the island's British governor-general, Sir Paul Scoon, according to the officials.