Motor Carrier Ratemaking Reform Act of 1979 - Stipulates that the antitrust laws shall not apply to pipeline or water carriers that are parties to a rate agreement approved by the Interstate Commerce Commission. Applies antitrust laws, relating to unlawful restraints and monopolies, to parties to a rate agreement where one of the parties to such an agreement is a motor carrier or freight forwarder. Declares to be reasonable a rate decrease or increase proposed by a motor carrier or freight forwarder which is no greater than seven percent above, or 20 percent below, the rate in effect on January 1, 1979.