Two hours before President Kennedy went on national radio and television at the height of the Cuban missile crisis in October, 1962, he showed congressional leaders secret U2 aerial photographs of Soviet installations to support his decision to order a blockade of Cuba.

But Kennedy decided not to display the photographs that night on television, according to Theodore C. Sorensen, a Kennedy White House adviser.

"He made a deliberate decision not to use them," Sorensen recalled. "He felt it had a certain sensationalism attached to it." However, the photographs were displayed later by Ambassador Adlai E. Stevenson at the United Nations.

Last night, President Reagan, seeking to inject U.S. public opinion with a new sense of urgency about the Soviet threat, took the opposite tack and showed similar aerial photographs to millions of Americans watching on television.

The four photographs purportedly showed a Soviet communications intelligence facility in Lourdes, Cuba; Soviet MiGs in western Cuba; Soviet weaponry at Sandino air field in Nicaragua and an airfield under construction at Point Salines in Grenada. The Nicaragua photo had been made public previously.

While such photographs have been shown at briefings for reporters over the years, Reagan went a step further last night when he used them as a prop in his Oval Office speech.

Since Kennedy's time, satellites have vastly improved U.S. intelligence-gathering. Reagan decided not to show the most sophisticated evidence of Soviet military activity, to avoid revealing sources and methods of obtaining the data, White House officials said yesterday. "These are not the most dramatic photos we could present because of our concern for revealing methods and sources of intelligence-gathering capabilities," said one official who spoke on condition that he not be identified.

The president has been urged recently by members of Congress and administration officials to declassify some photographs to justify his claims about the Soviet threat. But this selective declassification--a practice also used by other presidents--has been a target of criticism from Democrats.

This is because Reagan recently issued an order requiring government employes who handle classified material to sign non-disclosure statements and take polygraph tests upon request in an investigation of leaks.

"All of us have access to secret information," said Rep. Don Edwards, (D-Calif.), chairman of a House Judiciary subcommittee. "Yet, we are not privileged to selectively declassify it. He is declassifying only the information that will help his case."

Sen. Walter D. Huddleston (Ky.), senior Democrat on the Senate Intelligence Committee, said the public has "no way of knowing whether the information he releases and the classified photos he displays represent a balanced and objective view of the problem . . . . "