Washington — The sharp contrast in Pentagon and Kremlin defense policy was clearly illustrated this week in two unconnected but related bits of news.
At one of his relatively infrequent press conferences, Defense Secretary Caspar W. Weinberger explained the need to press ahead with such expensive and controversial weapons as the M-1 tank by saying he was ''a prisoner of a lot of decisions that have been made many years ago.''
He also cited this administration's decision to kill the Carter team's politically unpopular ''race track'' basing plan for the MX missile as a means of saving $15 billion, and noted with some weariness that yet another panel of experts is being convened to find a home for the MX.
On the other hand, according to a new Brookings Institution report, the Soviet Union has had no such political difficulties with its defense buildup. It has steadily developed several new generations of intercontinental ballistic missile, and has deployed its strategic ICBMs all over the Soviet Union with no concern about local opposition.
At his year-end press conference, the Pentagon chief pronounced himself ''reasonably well satisfied'' with the treatment his budget received at the hands of Congress. Lawmakers reduced the 1983 request of $257 billion by about $ 20 billion. But the Pentagon's expected goal for fiscal year 1984 ($285 billion) is unlikely to be met, given federal deficits approaching $200 billion and a Congress most of whose new members campaigned on less defense spending.
In order to blunt some of the expected criticism, Weinberger noted that while the administration originally had wanted to boost its predecessor's five-year defense spending bill by $116 billion, this increase now has been reduced to $75 billion.
He also cited 48 programs he said the Pentagon had canceled under his leadership. But most of these are relatively minor, and a recent internal Defense Department study shows that the Pentagon has historically underestimated the costs of major weapons systems.
''That may have related to the past, but not the present,'' Weinberger said in dismissing this finding of a civilian analyst at the Pentagon. ''It pointed up some lessons we hope and believe we've learned.''
On other matters, Weinberger:
* Echoed the remarks this week of chief US negotiator Edward Rowney, saying there is ''a good chance of securing an agreement in 1983'' on strategic arms reductions.
* Said there are no plans to increase the number of US marines in Lebanon, but he did not rule out expanding the American peace-keeping role ''as more territory opens up with this withdrawal (of foreign forces) process.''
* Noted the increase in Soviet strategic nuclear missiles and their widespread deployment, but said US officials aren't certain that these violate the unratified SALT II treaty.
* Noted the ''very substantial amount of money'' ($2.5 billion) that Congress approved for MX research and development and asserted that the missile ''certainly was not dead.'' He said the Pentagon would heed closely the advice of the new panel of former defense secretaries named to review MX basing, but stressed that the group was only ''advisory,'' and repeated his view that so-called dense pack basing still is the best of the many that have been considered.