The hard reality afflicting the Democratic Party the week before its national convention prepares to renominate Jimmy Carter was brought home to Democratic governors over breakfast here when Gov. Joseph Brennan of Maine voiced a prophecy of doom.

Brennan, the only governor endorsing Sen. Edward Kennedy for president, declared to the closed-door meeting "a disaster on a magnitude with 1972" awaits Democrats if President Carter leads the ticket. Not one of 21 avowed pro-Carter governors present disputed him. "I couldn't really hear very well what Joe was saying," one silent Carterite later explained to us. But he and others, in private, substantiated Brennan's prophecy. They were accepting it in a mood of fatalism.

Refusal by Democratic governors, attending the annual National Governors Conference, to join dump-Carter efforts does not stem from either faith in the president's ultimate political recovery or admiration for his leadership. As for Carter's insistence on a rule binding delegates to primary election results, some of his staunchest advocates consider it a blunder.

But they will not take personal risks to challenge the inevitable -- an attitude typifying governors of both parties the past two decades. Just as then-governor Jimmy Carter of Georgia played to an unresponsive audience at the Houston governors conference in 1972 when he warned of perils in George McGovern's impending nomination, so advocates of an "open convention" found no allies here.

Democratic congressmen who launched that movement a week earlier had counted on this Denver meeting to yield influential recruits. They had expected proselytizing led by Gov. Ella Grasso of Connecticut, a Carter backer who had apparently come out against the binding rule, and Gov. Hugh Carey of New York, who claims credit for the "open convention" idea.

That these congressmen were poorly advised to put their faith in governors soon became clear. Gene Eidenberg, the effective White House liason with the governors, soon had Grasso on the telephone; she informed him she really did not oppose the rule, only its enforcement, and therefore would vote with Carter for the rule. Grasso, who has had health problems, did not come to Denver.

Carey, often absent from governors conferences, did attend. At the breakfast meeting, he used his Brooklyn Irish eloquence to proclaim the inappropriateness of "loyalty oaths" for Democrats. He told how a former colleague in Congress, John Bell Williams of Mississippi, had been disciplined by House Democrats for disloyalty and then went home to be elected governor on the Democratic ticket. dCarey's performance was immensely enjoyed and totally ignored.

"I would say that Hugh Carey is not the most influential governor," one of his highly influential southern colleagues told us, in dry understatement, adding: "But he is probably a little more influential than the governor of California." Gov. Edmund G. Brown Jr., who for years has privately proclaimed Carter a sure loser in California, was on his good behavior here as part of his political rehabilitation program; he ventured no opinion on anything so political as the convention rules fight.

With the governors of New York and California discounted, big-state influence among the Democratic governors is negligible (the governors of Pennsylvania, Ohio, Michigan, Illinois and Texas are Republicans). The rest of the 31 Democratic governors are mainly from smaller states and do not share the same contempt for Carter's performance in office felt by Carey, Brown and many senior members of Congress.

Instead of contempt, there is a sense of futility about trying to guide the president. At the annual governors meeeting in Louisville a year ago, Democrats pressed hard for a Carter switch to bread-and-butter concerns (including priority for economic growth and energy development over environmental protection). There was no such talk in Denver. Nor did any governor press for a resolution praising the president's record in office.

There was private grumbling about tactics from Carter's most loyal supporters: liberal southern governors. Gov. Jim Hunt of North Carolina disagrees with Carter's insistence on the new rule binding delegates and considers it a sign of the president's intransigent morality unwisely applied to politics.

No governor is closer to Carter than Hunt, but he never has discussed this with the president. Nor has another important Carterite, Gov. Bill Clinton of Arkansas. Burdened with the serious drought crisis, Clinton told us he had not had time to either approve or not approve of the president's adamant position on the rule.

The star of Denver was not a governor but Carter's campaign chairman, Robert S. Strauss. He put on a virtuoso performance at the breakfast, vigorously invoking personal ties, loyalty to the president and even patriotism in behalf of binding the delegates. "It was a helluva show," one admiring governor told us. It was also overkill. Strauss was talking to an audience that, probably moved more by fatalism and futility than loyalty, had no intention of making more trouble for the president.