Leningrad University has not acknowledged receipt of a letter written last June by President Pusey, according to a reliable source outside the University. The Pusey letter outlined in detail a program for the implementation of the cultural exchange agreement between the two institutions.

The Russians' failure to respond is not regarded as precluding a future agreement. It is thought that "waiting to see" the results of Premier Khrushchev's visit to the United States may have contributed to the delay.

Richard E. Pipes, Associate Director of the Russian Research Center, commented last night that the Soviet inaction is "not fatal" to the success of negotiations. He and other officials of the Center felt that some definite arrangement will be produced in the next few months.

The Harvard-Leningrad program, announced last winter, was the first interinstitutional step under the general Lacey-Zaroubin agreement worked out two years ago. An affiliation between Columbia and Moscow University followed shortly after the Harvard move, and Yale recently made public an exchange agreement with the University of Kiev.

Five Harvard professors visited Leningrad last February as the first peliminary step in the exchange program, and a group of Leningrad faculty members returned the visit a month later. At the time of the Russians' stay in Cambridge, representatives of the two institutions "reached very broad agreement on general principles" of the exchange, according to Pipes.

The Lacey-Zaroubin agreement between the two governments expires next January, and negotiations on renewal and amendment of the pact will probably open in Moscow later this month.