Charging that approval of the Reagan administration's $100 million aid package to anti-Sandinista guerrillas constitutes a heightened threat to Nicaragua, President Daniel Ortega today called for intensification of security measures under a state of emergency.

Ortega's announcement, in the form of a communique issued by the nine leaders of the ruling Sandinista Front, followed a government order closing the country's only opposition daily, La Prensa.

In a three-line letter, government censor, Capt. Nelba Blandon notified the newspaper's editor that it would be closed for "an indefinite period of time." The newspaper is regularly censored and has been closed down for a few days at a time in the past.

Reading the Sandinista communique on national radio and television, Ortega said, "it is indispensable to increase and reinforce the security measures that allow the country to defeat the terrorist plans that the mercenary forces of President Reagan will resort to."

He called the approval of the aid to the contras a situation of "unpredictable seriousness" that would demand a "strict and severe" application of the state of emergency.

Saying the state of emergency had been applied in the past with "excessive flexibility," Ortega said the government would use all necessary political mechanisms to counteract any front groups acting on behalf of the rebels, known as contras, or counterrevolutionaries.