No doubt it's partly because of the political year in the United States, partly the standoff in US-Soviet arms control parleys - but we distinctly sense that the nuclear debate is settling again into the bones of deepest debate over fundamental strategy.
President Reagan's ''star wars'' research proposal is the new cutting edge of the longtime debate between advocates of new defense missile systems and those who want to restrict nuclear arsenals to offensive weapons.
We'll say at the outset that a reelected Ronald Reagan with a GOP Senate majority can probably count on enough public support for his missile defense program, if its characterization as a strictly research-and-development, err-on-the-side-of-security, two-decade-development venture holds up. Moderates among arms experts say the Reagan nuclear budget doesn't show the kind of expansion that would suggest preparation for a crash defensive nuclear arms race. That's as it should be.
The President's position is coming under severe attack that could lead to a rough partisan set-to during the campaign. Still, given the seriousness of the nuclear arms issue, one has to welcome the kind of weighing in on the subject that Gerard C. Smith gave in a speech Feb. 2 at the Fletcher School of Law and Diplomacy. Smith, who helped negotiate for President Nixon the SALT I treaty, argued that a dangerous ''deregulation'' of strategic nuclear arms is under way; a defensive system like ''star wars'' would destabilize the existing strategic balance; moving ahead on a nationwide defense would abrogate the ABM treaty; an effective nationwide defense capability ''is an impossibility.'' Further, Smith warns that whatever Mr. Reagan's ''idyllic'' concept of a future when the superpowers would forsake offensive weapons because defensive systems would make them obsolete, others around him really aim ''for defenses in addition to offensive forces, not as a substitute for them,'' to regain strategic superiority.
Smith acknowledges the pragmatic political realities outlined above: He would ''keep 'star wars' in a prenatal condition of research and development.''
Where the momentum of research and development crosses the line into deployment - violating the existing ground rules - is indeed a worrisome question. Here, whatever his spending plans might suggest, Mr. Reagan's rhetorical excesses might give the Soviets a wrong impression, arms analysts say. The Soviets themselves are showing a split personality on the subject of defensive programs: Their military is well into them, despite ideological disavowal. The Soviets are now debating Reagan's intentions - whether he's serious about sticking to the offensive nuclear standoff, and pursuing the defensive possibilities chiefly for effect. Reagan has been sticking to the ABM treaty, which was renewed last year. Research on defensive systems has been under way ever since President Nixon left research and development in the treaty as part of the price of getting it passed.
Now the other side: Many in the armed services, particularly the Navy and Air Force, favor a defensive missile program. As Smith points out, it has a constituency in the arms industry who see billions of dollars in contracts in the next two decades. Nothing surprising here.
But it has its backers for strategic reasons too. Seymour Weiss, an experienced security affairs consultant, contends it makes sense for deterrence. ''The essence of deterrence is to enhance the uncertainty of an attacker,'' Weiss says. ''Or let's assume deterrence doesn't work and war starts - as history shows wars do - would we rather not have any defensive capability at all?''
The heart of the debate is between those like Smith who would restrict nuclear capability to, say, targeting cities; and those who prefer a mix of targets and systems, who advocate nuclear instability and complexity. To the former, mutual assured destruction (MAD) of restricted targets helps keep the two nuclear scorpions, the US and the Soviets, from launching a mutually suicidal attack. To the latter, ''star wars'' is a natural progression.
Under Nixon, after long and acrimonious debate, Congress narrowly passed a bill to build a system to defend the Minuteman missile - whereupon the same administration signed an arms control treaty that all but outlawed it. The ABM program got Senate approval because of Democrat Henry M. Jackson and a handful of other Democrats. The best Mr. Reagan can do for now is to keep his defensive missile program under explicit research-and-development constraints.