The latest periodic Pentagon report on Soviet military might - released yesterday - is as important for its timing as it is for its content. It is chock-full of new data on Soviet weaponry and Warsaw Pact-NATO force comparisons. But it is also a back-to-basics primer on how and why military thinking and activity pervades the Soviet Union, from the Kremlin to industrial sites and from research facilities to Red Army outposts scattered throughout the country and - increasingly - beyond.
This latest edition of ''Soviet Military Power'' needs to be viewed against the backdrop of worsening US-Soviet relations, the growing proclivity of lawmakers to cut defense spending, and continuing questions here about the ''steadfastness'' of European allies in the face of Soviet expansionism. It thus will be a key tool this election year in President Reagan's calls for commitment and resolve on national defense.
There are revelations in this 136-page report, which is notably longer than those issued in 1981 and 1983. Among them: two new classes of attack submarine using hull design and materials years ahead of the United States sub fleet; two new jet fighters with advanced radar capability enabling them to shoot down low-flying cruise missiles, as well as aircraft; the testing of two fifth-generation intercontinental ballistic missiles, which may violate arms control agreements; a continuing increase in deployed SS-20 medium-range nuclear missiles; a new, and for the Soviets the first, large nuclear-powered aircraft carrier; ground-based lasers that may be able to attack US satellites; and a buildup in military stockpiles in the Far East that now nearly matches those positioned against Western Europe.
Senior defense and intelligence officials say they are particularly worried about advances in Soviet research and development, which now are encroaching on the traditional US leads in advanced technology. At the urging of conservatives in the US and Western European defense officials (who were critical of the ''cartoons'' used in earlier editions of the report), this new edition discloses more classified data than in the past, including photos obtained from intelligence sources inside the USSR.
''We tried to take the most leading-edge classified information that we could get released,'' says a senior defense official. ''Until yesterday, this was all included in our classified files.''
This report comes just as Mr. Reagan and other senior administration officials have been raising fundamental questions about the role of Congress in foreign affairs (especially the use of military power), as the Soviet Union moves to fill the void in the Middle East left by the US failure in Lebanon, and as the administration steps up military activity in Central America.
In an address last Friday, the President criticized Congress for failing to develop ''capacities for coherent, responsible action needed to carry out the new foreign policies it has taken for itself.''
While not suggesting that this country's relatively untidy democratic system is an obstacle to US influence abroad, the Pentagon report outlines a vast Soviet system of military power unhampered by public dissent or legislative criticisms. All men up to age 50 are subject to military service, and Soviet women can be drafted in time of war.
In a speech to the Harvard Club of Washington this week, Defense Secretary Caspar W. Weinberger warned against ''the undercurrent of isolationism that has never been far from the surface in American foreign policy.''
In outlining for Pentagon reporters the latest Defense Department document on Soviet military power - particularly the new offensive weapons being developed and produced - he said the purpose behind the steady buildup there is ''world domination.'' Mr. Weinberger's press conference was broadcast live to Western Europe, and a few moments later he answered questions by satellite from European journalists.
Weinberger cited the ''enormous power projection capabilities'' of Soviet forces and - recalling continued pressures in Poland, the 108,000 Soviet troops in Afghanistan, and the shooting down of a South Korean airliner last year - the willingness to use such power.
Continuing the theme of Reagan's recent foreign policy speech, ''Soviet Military Power'' calls for ''demonstrated commitment'' and ''consistency in our resolve'' to prevent the Soviet Union from using its military capability to gain political advantage. The report details Soviet military activity in Grenada and, through other Warsaw Pact countries and Cuba, in Nicaragua.
The first edition of ''Soviet Military Power'' was criticized for being one-sided. The updated version includes NATO/Warsaw Pact force comparisons and acknowledges that the US - particularly when allied military assets are included - is clearly ahead in some weapons. For example, NATO has 1,500 warships, the Warsaw Pact 1,400. And in ships over 1,000 tons displacement, ''the United States and its allies hold a significant lead.''
In comparing objectively military balance of power, experts point out that important nonquantifiable factors must be included: the fact that NATO is a true defensive alliance freely entered into by its members, and therefore presumably more reliable in time of war. It also is generally agreed that an attacker typically needs three to four times as big an arsenal as the country or countries he is attempting to invade.
There have been in recent years what Weinberger disparagingly calls academic disputes between the Central Intelligence Agency and Defense Intelligence Agency over a perceived flattening in the rate of increase in Soviet defense spending. But there is no argument among US intelligence sources that Warsaw Pact weapons deployment surpasses that of NATO. For example, NATO produced 1,650 new tanks last year, the Warsaw Pact 2,700. For new fighter-bomber aircraft, the numbers were respectively 675 and 950. For this reason, Weinberger argues, ''We have to make - all of us, the European allies - very large and what are clearly very unwelcome efforts to regain deterrent strength.''