It was a week designed to wear out skirts and trousers and to numb the mind with acronyms - from ALCM to FROD to GLCM and SLCM. It was also a week that nicely - if not neatly - set the stage for the great debate on the strategic arms limitation treaty, which has an acronym of its own, SALT II.

Four long days of hearings before the Senate Foreign Relations Committee left all the issues open, but they led to one important truth: the burden of proof is not on the treaty's proponents, who have been on the defensive for two years, but on the opponents who would prefer to change it radically or reject it altogether.

The opponents face a practical problem that may not be insurmountable but poses a big political challenge: to convince the Senate, or 34 of its members, the number needed to block ratification, that the United States would be safer by risking the collapse of the SALT process than by accepting this SALT treaty.

Put another way, the opponents' challenge is to argue successfully that a world without SALE might be better for the country than a much more familiar world - really an extension of the status qup, at least in the short run - that would accompany approval of SALT II.

Two articulate opponents of SALT II testified last week.

Paul H. Nitze suggested that a world without SALT might be an improvement, because it would mobilize America to get serious about keeping ahead of the Russians. Recently retired Lt. Gen. Edward J. Rowny offered another way out: reopen negotiations. The Soviets need SALT more than America does, so they will be willing to start negotiating all over again, he assured the Senate committee.

Neither alternative seemed to electrify the Foreign Relations Committee. Richard G. Lugar (R-Ind.), whose views seem to coincide with Genl Rowny's on many points, told him it would require "a leap of faith" for the Senate to adopt his optimism that after seven years of negotiating SALT II, the Russians would willingly start over again. Rowny himself said later it might take one year or as many as six to negotiate a new treaty.

As to living without SALT altogether, senator after senator asked witnesses in the hearings what the advantages of that might be. They were told of only one, beyond Nitze's general belief that the country needs a good scare.

The one advantage, also mentioned by Nitze, is the unquestioned ability to build a new missile system in which 200 or so supermissiles would be shuttled around among 2,500 or more silos in a deceptive "shell game" meant to fool the tsoviet Union's targeters. This might be precluded by SALT II. The Carter administration seems to favor another method for hiding new supermissiles from the Russians by putting them in open trenches covered at intervals by shelters.

The Joint Chiefs of Staff gave testimony on Wednesday that was widely and accurately reported as a lukewarm endorsement of SALT II. But they were explicit on two points that are central to the opposition's political dilemma: they did not favor trying to reopen negotiations on important substantive issues, and they did not favor a world without SALT. Their carefully drafted and well-written formal testimony said that the treaty's "specific limits on the United States are quite nominal" and will allow building all the new weapons the chiefs say they need.

The opponents' best gambit is to try to avoid a choice between SALT II and no SALT by proposing amendments to the treaty. This is the course that even the most irreconcilable opponents will follow.

Wholesale amendments that alter the central elements of the treaty would amount to an unmistakable demand for reopening the negotiations. But there are critics of SALT II who hope to devise amendments that don't raise that spectre so starkly.

Minority Leader Howard H. Banker Jr. (Tenn.), for example, has said repeatedly he will not support "killer" amendments to the treaty, but says, too, that he wants it altered substantially.

It remains to be seen where the Senate will draw the line on changes to the treaty. There is no doubt at all that changes will be made. The Foreign Relations Committee is already inclined to add four or five reservations and understandings before it sends the treaty to the floor.

The White House correctly fears that at some point an amendment will emerge that is both irresistible to a majority of senators and unacceptable to the Soviet Union. The administration hopes its witnesses and Senate allied will maintain enough pressure on uncertain senators to at least insure that they don't vote # for substantive amendments without realizing what they might mean for the fate of SALT.

The Joint Chiefs' lack of enthusiasm for SALT II was right in step with the general mood of the Foreign Relations Committee. Enthusiasm so far in these hearings has been as rare as short-winded testimony; frustration is common.

Some senators are frustrated by the discovery that Soviet strategic weapons are now so good and so numerous that discernible course could lead America back to clear strategic superiority.

Others are frustrated that they did not foresee the present state of affairs and do something years ago. "We've been goofing off for 10 years," Sen. Jacob Javits (R-N.Y.) complained at one point - and later iterations of American activity in that period did not appear to change his mind.

Sen. George McGovern (D-S.D.) is frustrated that the SALT debate seems destined to produce expensive new strategic programs that he thinks are superfluous and dangerous. McGovern argued his position forcefully all week.

McGovern was one of several senators who made strong impressions last week. Another was Joseph Biden Jr. (D-Del.), who has spent long hours trying to master the details of SALT, and who gleefully did battle with Sen. Baker. Biden did more orating than interrogating, however.

Howard Baker's role was the subject of much comment. Some friends were alarmed at his performances on the first and second day, when he seemed to make large issues out of small or confused points. But Baker's reputation as a clever politician protects him from ridicule. Members of the committee and its staff speculated intensely about what Baker might be up to. He himself decided not to take part Wednesday and Thursday, when the joint chiefs and critics of the treaty testified.

An informal poll of spectators in the cavernous Senate Caucus Room suggests that Defense Secretary Harold Brown was the most effective witness of this week. His former subordinate, recently retired general and SALT negotiator Rowny, who criticized the treaty, also did well.

Chairman Frank Church (D-Idaho) held the committee to its schedule and led the questioning of witnesses with authority. But Church skipped the Thursday afternoon hearings for more pressing business: an Energy subcommittee's markup of his own bill to encourage the use of gasohol.