Among the major network news operations, only CBS is balking at broadcasting Soviet leader Mikhail S. Gorbachev's New Year's message today to the American people in full, spokesmen said Wednesday. CBS decided against showing the entire Gorbachev speech, but "will use appropriate excerpts on our news broadcast," spokeswoman Donna Dees said Wednesday. All three networks plus Cable News Network plan to air President Reagan's address to the Soviet Union. Gorbachev's greeting, expected to be three to five minutes long, is being made available to the networks as part of a reciprocal agreement between the United States and the Soviet Union. "Our feeling was that they were significant and they should be seen in their entirety," ABC spokeswoman Carol Olwert said. NBC spokesman Andrew Freedman said network executives viewed the Gorbachev message Wednesday afternoon "and we decided it would be of interest to the viewers." The Soviet leader's address will be made available to local television stations as well.