At this point in a presidential campaign, "momentum" is the holy grail, and in the wisdom of television-age politics, momentum goes to the candidate who can "go on the offensive."

Because this is the television age, being "on the offensive" -- or "on the defensive" -- must appear on television to be real. So what's on television?

This week what's been on television is Ronald Reagan on the defensive. Also on television is an extraordinary amount of talk, mostly by the reporters covering the Reagan and Carter campaigns, about who's on the offensive. Sometimes it sounds like a continuation of the deodorant commercials.

NBC's Chris Wallace, covering Reagan, began this talk Monday night: "Throughout the campaign, Reagan has tried to stay off the defensive," Wallace reported. "But the peace issue has become so damaging he will spend most of this week talking about it, hoping to persuade voters their real worry is domestic issues."

The in-no-way peaceful "peace" issue was indeed the topic of the week, introduced by Reagan Sunday night in a half-hour television address on the CBS network. That speech was itself a defensive act, an admission that President Carter was scoring points by raising fears that Reagan would make a dangerous president. So perhaps it was no surprise that Reagan remained on the defensive for the rest of the week. But the way it played out, Reagan's own statements, some planned and some ad-libbed, aggravated his problems on the tube.

"On Monday night Reagan personally decided to "go on the offensive" on a foreign policy issue that hadn't previously been considered part of the "war and peace" rubric, the hostages in Iran.

Reagan's Monday-night comment that he could not understand why 52 Americans have been held hostage for nearly a year came at the end of a long day of showmanship that was meant to reassure voters that he was a moderate, peace-loving man. To do that he brought along former secretaries of state Henry Kissinger and William Rogers and other moderate Republicans from past administrations so they could all tell the television cameras how reasonable Reagan was.

How well this worked is problematical. "He is not a warmonger," former secretary Rogers assured NBC's cameras, a formulation evoking the famous Nixonian disclaimer ("I am not a crook") that may not have benefited Reagan's cause.

"Aides acknowledge that Reagan is having trouble shaking the perception that he might be militarily reckless," Barry Serafin reported on ABC Monday night. Wallace on NBC said Reagan was trying to "ease concerns that as president he would start a war." The reporting wasn't hostile to Reagan, it just dwelled on this war-peace problem the candidate has.

In any case, Monday's Kissinger-coated lozenge of reassurance quickly dissolved in the furor set off by Reagan's comments on the hostages which he sharpened and elaborated for the television cameras Tuesday morning. The Tuesday night shows all made big news of Reagan's decision to raise the hostage issue, and of his statement that he had "some ideas" for how to get them home. What ideas? Reagan refused to say, correspondent Jerry Bowen reported to CBS.

Added Bowen: "Reagan's raising of the hostage situation reflects a concerted effort on his past to turn the corner on the umbrella issue of the campaign -- war and peace -- an effort to place Mr. Carter on the defensive." c

Did this work? The answer lies in the eye of the beholders out there in television land. Obviously some Americans share Reagan's belief that the year-long hostage episode is "a humiliation and a disgrace" for the United States, as he put it Tuesday, and conceivably Reagan scored some points by casting the issue in those terms at a moment when the news shows were all reporting signs that the hostages might soon be released.

But by the Wednesday night network news programs, Reagan was looking very much in the defensive again:

On CBS, Jerry Bowen opened his report like this: "Reagan began his day retreating from the hostage issue he raised earlier in the week." Said Bowen, "Regan acknowledges the war and peace issue has hurt him."

On NBC, Chris Wallace reported that, "This morning, Reagan backed out of the hostage controversy that he started two days ago, refusing to answer any questions on the subject." Wallace said Reagan acknowledged that Carter had been successful in creating "a warmonger image of him." And in his closing comments, Wallace introduced a new "negative" for Reagan. Noting that Reagan would be spending the final days seeking to win over undecided voters, particularly women, Wallace added: But today he may have suffered a setback. Reagan announced formation of domestic task forces with 329 advisers. Fewer than 25 of them are women." Added abruptly at the end of Wallace's daily report, this must have baffled some viewers, but the important point may be that it sounded bad for Reagan.

On ABC, Serafin began: "Aides insisted that the issue had not boomeranged, but Ronald Reagan today announced that he would have nothing more to say about the hostages. . . ."

Thursday night the correspondents were still taling about Reagan's problems. on NBC Thursday, viewers learned that "Reagan is trying to make Mr. Carter the issue, but today he started a new issue of his own, telling the Detroit News he would declare the Panama Canal treaty null and void if the canal's neutrality were threatened." On ABC, Reagan assured elderly voters he "would not make Social Security voluntary," a reference to another Reagan negative. On CBS, Reagan aides worried about how the return of the hostages would affect the election.

President Carter's week on television went a lot better than Reagan's, if only because the president got a lot of airtime to flail his opponent and try to sound presidential on the hostage issue. Carter's crowds seemed responsive, and the president looked in better form than he did earlier in the campaign.

But wait 'til next week -- seriously. Next week, when the candidates debate head-to-head, the real dice will be thrown for the prize George Bush used to call "Big Mo," the serious momentum that will carry either Carter or Reagan to the presidency.