Defense Secretary Frank C. Carlucci said Monday he will travel to Moscow in early August for his third meeting with Soviet Defense Minister Dmitri Yazov, and the second-ranking Soviet defense official will tour the United States in July. The exchange of visits is aimed at reducing military tension between the superpowers as part of a general widening and improvement in the U.S.-Soviet dialogue. In the first business session between the Soviet and U.S. defense secretaries, Carlucci and Yazov met in Bern, Switzerland, last March and for a second time during the Moscow summit May 31-June 2. The ``dialogue is not valuable for its own sake, but only as a means to enhance our security,'' Carlucci said in a speech at the National Press Club. ``Our discussions in Bern and last month in Moscow were candid and, I think precisely because of that, constructive.'' ``We have gained a great deal from having an opportunity to air our differences, and to explore ways that we might improve our relations,'' he said. ``As in our earlier meetings, our agenda will include exploring ways to avoid dangerous military incidents, and to expand military-to-military contacts.'' The Soviet first deputy defense minister, Marshal Sergei F. Akhromeyev, will make a July 5-11 visit to the United States at the invitation of Adm. William Crowe, chairman of the U.S. Joint Chiefs of Staffs, the Pentagon and Soviet news agency Tass announced. Akhromeyev was in Washington last December for the summit, but the upcoming trip, ``will be his first visit outside the nation's capital,'' the Pentagon announcement said. Akhromeyev, the Soviet chief of staff, ``will tour military units from all four military services and will travel to Virginia, North Carolina, Texas, Oklahoma, South Dakota and New York during his visit,'' it said. Crowe and Akhromeyev will have joint news conferences on July 6 and July 11, and on July 11, the Soviet marshal will address a meeting of the Council on Foreign Relations in New York City. Akhromeyev will not be allowed to view any classified training or equipment, the Pentagon said, but he will visit Camp Lejeune, N.C.; the aircraft carrier USS Theodore Roosevelt; Fort Hood, Texas; and Ellsworth Air Force Base, S.D. The Soviet defense official will be allowed to view a new B-1B bomber, but will not be allowed to fly in one, the Pentagon added. In his speech, Carlucci said he was skeptical of the reform rhetoric of Kremlin leader Mikhail S. Gorbachev and of Soviet claims that ``they are shifting to a purely defensive military posture.'' ``For my part, I have indicated that the United States would welcome such a shift, but that in spite of Soviet claims, we see no change in the Soviet force structure and no reduction in resources devoted to the Soviet military, which continues to absorb between 15 and 17 percent of the Soviet'' gross national product, he said. ``Now is not the time to let down our guard,'' he said. ``There is every reason to believe that the Soviets see in our technology a way to derive not only economic but military advantage.'' ``If the end result of reform is a Soviet Union that is less expansionist, that reduces the resources it now devotes to the military, that delivers on its promises to respect fundamental freedoms and human rights, that is more open to dialogue with the West, then change will have been for the better,'' Carlucci said. ``On the other hand, if the end product of Soviet restructuring is nothing more than the development, perhaps even with Western assistance, of a stronger Soviet military machine, then we in the West will face a far more dangerous threat than we do at present,'' he said. An aide to Carlucci said that the exact dates and interinary of the trip to Moscow would not be announced until next month.