There are no plans for a fifth summit between President Reagan and Soviet leader Mikhail Gorbachev at the United Nations this fall, a Soviet government spokesman said Tuesday. Gennady Gerasimov also said that Gorbachev and Foreign Minister Eduard Shevardnadze are on vacation. Gerasimov, responding to rumors that a meeting might take place between the U.S. and Soviet leaders at the opening of the United Nations General Assembly this fall, said "the Presidium has not yet approved the composition of the Soviet delegation."