FROM the first heated moment in the initial debate it was clear that George McGovern, who had been through it all before, would be the calm elder statesman of the Democratic presidential candidates. When the atmosphere turned acrimonious he quietly counseled his colleagues against so sharply attacking one another. Implicitly noting that many of the barbs had been aimed at former Vice-President Mondale, he wryly reminded the others that ''sometimes front-runners do get nominated.''
But the McGovern candidacy, now ended, was more than a nostalgia trip for the man who, as his party's presidential nominee in 1972, had won only Massachusetts and the District of Columbia in a campaign based on his opposition to the Vietnam war. Somewhere along the way this year he became known as ''the conscience'' of the Democratic Party.
It was a concept to which he referred when he withdrew from the race Tuesday night after finishing third in Massachusetts despite two weeks of intensive effort. ''This is not a concession speech,'' he said in the relaxed manner that typified his candidacy this time. ''No campaign could ever claim a greater victory than to emerge from a campaign with the title of conscience . . . and peacemaker.''
There was genuine affection between McGovern and voters of all ages, as the former South Dakota senator - who lost a reelection bid in November of 1980 - impressed a new group of American voters with his character and views. But the warmth did not translate into enough votes. He was forced to the sidelines with former candidates Alan Cranston, Reubin Askew, and Ernest Hollings.