In 1976, Jimmy Carter accepted the Democratic nomination for president with a speech that was simple and direct. "Out nation's best is still ahead," he promised. It was, as many said then, a masterful preacher's sermon.

Thursday night Carter gave an engineer's speech, a speech constructed like a building or a ship. Carter and his aides obviously had thought of all the points they could make to defend an unpopular president, then drew up a list of criticisms of Ronald Reagan. They pasted them together and Carter recited them all.

As political theater, the two performances were hardly comparable. The preacher of 1976 put on the better show. "I am wiser tonight than I was four years ago," Carter the engineer said this time, but with a wisdom has come a lot of other baggage. Carter this year was defensive. In 1976 he had a vision to sell, in 1980 he has an unpopular record to defend.

In four paragraphs near the beginning of this year's speech, the president returned eloquently to the vision he sold the country in 1976. "I see a future of economic security . . . I see a future of justice . . . I see a future of peace," he promised.

Four years ago he used these words: "I see an America on the move again, united, a diverse and vital and tolerant nation, entering our third century in pride and confidence . . ."

In 1976 this struck a chord that reverberated sympathetically throughout the land. Four years later the same message provokes skepticism.

In 1976 Carter spoke just a few days after the nation's Bicentennial birthday party. It was a time of good feelings and high hopes. The biggest story of that month was the odyssey of the tall ships plying the East Coast to celebrate the Bicentennial. Carter rode the same waves.

Because it was such a good sermon, the 1976 acceptance speech wasn't judged on rigorous intellectual criteria. It was filled with billowy passages:

"It is time for America to move and to speak not with boasting and belligerence, but with a quiet strength; to depend in world affairs not merely on the size of an arsenal, but on the nobility of ideas; and to govern at home not by confusion and crisis, but with grace and imagination and common sense."

Those hopeful words were spoken by a man who had never tried to run a country or a foreign policy. Thursday night's speech may have been a more honest document, with fewer flowing passages and numerous references to specific programs and statistics. But by being in this sense more honest, it had to be less hopeful, less inspiring.

In fact, President Carter in 1980 had to try to explain why he had not become the sort of leader Jimmy Carter promised to be in 1976. This is what he said:

"We have made tough decisions and we have taken the heat for them. We have made mistakes, and we have learned from them. Now we have built the foundation for a better future."

Not surprisingly, this 1980 Carter sounded much more defensive. Carter's 1976 acceptance speech contained no negative references to his likely (but then not yet nominated) opponent, Gerald R. Ford. It was entirely a positive statement.

About a fourth of last night's speech was devoted to lambasting the Republicans and Ronald Reagan. If the Grand Old Party should win in November, Carter said, "I see despair . . . I see surrender . . . I see risk." He also sees repudiation, of course, which explains his defensiveness. r

In 1976 Carter made old fashioned political promises. In his acceptance speech he promised "an efficient, economical, purposeful and manageable government . . . and you can depend on it." He promised to reform the tax system -- "a disgrace to the human race" -- "and you can depend on it." Thursday night there were no such specific promises.

Carter's acceptance speech in 1976 was a magical moment, perhaps the high point of his political career. Carter spoke quietly that night in the lilting cadence of a Baptist preacher with a sure sense of himself and his message.

Carter could not find that preacher's rhythm last night. He shouted his way through his long speech, straining, it seemed, to evoke the kind of excitement in the hall that Sen. Edward M. Kennedy created on Tuesday. This is not what Jimmy Carter does best.

There was no magic in Thursday night's speech. Instead, a weary convention heard the sounds of slogging from a worried politician who knows he is in deep trouble.