Washington — The Reagan administration will vigorously continue its nuclear weapons buildup as long as the Soviet Union does not agree to substantial reductions in such arms, and it will keep pushing for modernization of US strategic systems in any case.
It will ''put all of the resources (it) possibly can'' into space-based strategic defenses and not use its technological advantage merely as a ''bargaining chip'' to force cutbacks in large Soviet intercontinental ballistic missiles.
The administration will not seek an arms control agreement for its own sake, and it may overlook current restrictions on submarine-based missiles if Moscow is not more forthcoming at Geneva.
Making these points in an interview with The Christian Science Monitor, US Defense Secretary Caspar Weinberger stressed the patience and ''great resolve'' of the Reagan administration regarding what has become one of the key issues in the presidential campaign: nuclear weapons and arms control.
On the eve of his departure to meet with NATO defense ministers this week, Secretary Weinberger also outlined how he thinks Soviet behavior has been influenced or modified by this administration's defense and national-security policies, described the differences between Walter Mondale and Ronald Reagan on conventional deterrence and overall military strategy, and responded to the harsh criticism of Pentagon procurement and management policies.
Mr. Weinberger's comments on arms control efforts put into perspective the election-prompted hints by some senior officials that the United States is ready to offer ''flexible positions'' and ''imaginative options'' if the Soviets return to the stalled Geneva talks. They also give clues as to the likely US bargaining attitude in 1985 (presuming Reagan is reelected). This will be of increased interest because the SALT II strategic arms limitation agreement expires next year.
''We have not in any sense relaxed the necessary modernization of the strategic triad,'' Weinberger said, referring to land-based missiles, submarines , and bombers. ''We have to keep that and we have kept that.
''If we are able to obtain a thoroughly reliable strategic defense, then certainly one of the hopes is that you could have substantial reductions in offensive systems,'' he went on. ''But our obligations to Europe, our obligations to ourselves and to our own people - to free peoples everywhere - is to that kind of strategic umbrella that will deter the Soviets from using their immense and growing nuclear strength.''
Weinberger ticked off the advances in ''accuracy, yield, and ability to deliver'' US strategic weaponry made in recent years, advances that have left the US ''vastly stronger.'' Among these are new Trident submarines, the B-1 bomber, ''very good and interesting results'' with cruise missiles, and especially the ''astonishing'' accuracy of the MX missile, which will be able to destroy ''hardened targets.''
''So I would hope we have their attention,'' he said, referring to the Soviet attitude toward eventual arms reductions.
Pointing out the changes Washington has made in its negotiating position, Weinberger dismissed as ''total nonsense'' charges that the Pentagon has sabotaged fruitful nuclear arms negotiations. And he emphasized that, based on his 20-year personal relationship with Ronald Reagan, he firmly believes that the President does want to reduce nuclear arsenals.
At the same time, however, he acknowledged that Reagan's arms control ideas - especially when tied to the push for advanced missile defenses - represent a ''revolutionary concept'' that ''violates the conventional wisdom.''
Holding to the theory of ''mutual assured destruction'' and rejecting the possibility of defending against nuclear attack, he said, is ''an example of conventional wisdom run rampant and an example of why conventional wisdom is so unwise.''
He scorned past arms control agreements which, he said, allowed a steady buildup in Soviet nuclear weapons. And he dismissed the kind of negotiating flexibility that ''translates into giving the Soviets much more of what they want in order to get them to sign a piece of paper.''
''The critical factor here is that the SALT agreements and all of the other agreements have allowed for expansion, and the Soviets have taken advantage of that to the fullest,'' Weinberger said. ''The President wants a decrease and he keeps going back to that. And if that is (being) inflexible, then that's a good kind of inflexibility.''
The Reagan administration is about to release a report detailing ways in which the Soviet Union is alleged to have violated SALT II and other signed arms agreements. Presumably, the United States itself (which never ratified SALT II) will be even less inclined to abide by the 1979 accord in coming months.
The US has been deploying new Trident submarines at the rate of about one a year. Some analysts warn that unless older missile-carrying boats are retired, the US will violate the agreed-upon limit on submarine missiles.
In the interview, the defense secretary refused to rule out the possibility that this might be the case. ''We have adhered generally to the terms of SALT II ,'' he said. ''But I just wouldn't get into any hypothetical (question about future Trident deployments).''
In terms of overall military strategy, Mondale has yet to detail how his would clearly differ from Reagan's. Under a Mondale administration, US commitments abroad apparently would not change much, even though the Democratic challenger would cut the Pentagon's budget $25 billion by 1989.
''Everybody pays homage'' to a strong national defense, Weinberger said, ''but the important thing is what would be done about it.''
Noting the nearly complete acquiesence by the US Congress in approving the administration's defense buildup (notwithstanding plenty of verbal opposition), the defense secretary cited the ''tremendous differences in attitude ... tremendous differences in resolve'' between the candidates.
''As a result of that, (Reagan) has obtained major increases that could not otherwise have been obtained,'' he said. ''And I don't see anything resembling that in the other candidate.''
Regarding Soviet expansionism, Weinberger said ''a pattern of behavior in the '70s has changed and that, I think, is significant and important.'' He said the Soviets are ''doing very badly and taking quite heavy losses'' in Afghanistan and apparently ''aren't willing to increase the military activity even where they're doing that badly.'' He also said that ''we were very much closer to an invasion of Poland in December of 1980 then we are now.''
''We have to think that that change in pattern of activity is related to the correct perception that the United States is regaining military strength and is continuing to do so and has the will and resolve to continue to do so.''
He acknowledged a ''continuation of (Soviet) attempts to secure bases in (Central America and the Middle East) by proxy. ''But the Soviets themselves do not appear to have increased their effective acquisitions, and they've suffered a setback in Grenada, a very major one,'' he said. ''So in addition to no additions, they've had this negative in Grenada.''
Since the outset of the administration's push to ''rearm America,'' there has been persistent and unusually harsh criticism of Pentagon procurement and management practices. Much of this has come from conservative as well as moderate Republicans on Capitol Hill.
As he has in the past, Secretary Weinberger complained that such critics frequently overlook progress made by the administration.
''What bothers me particularly is ... that if we get convictions, if we take contractors off the list, if we report all the things that we've done to make recoveries and refunds, nobody ever stands up and says 'this is a very good thing,' '' he said.
''It's a good, cheap demagogic shot if you don't worry about the facts,'' he said.