Ronald Reagan's acceptance speech marked the end of a political journey that began with another oratorical flourish 16 years ago. The differences between those two speeches help explain why Americans who call themselves conservatives think they have a winner in 1980.

The basic difference is simple enough: In 1964 Reagan saw a sinking America that was squandering its freedom and indulging a government that threatened to "impose socialism upon a people." Thursday night Reagan described an ailing America that could be redeemed -- could be returned to the glories of an earlier era, the early 1960s, for example.

The new Reagan sees hope and opportunity where the old one could see only despair, and that may explain why he is ahead in the polls. The candidate for whom he spoke 16 years ago -- Barry Goldwater -- never came close to the hearts of a majority of his countrymen. The new Reagan reaches out, hoping to be a president; the old Reagan was defending a dying candidacy.

The Goldwater campaign gave Reagan his first moment of national political prominence. It came on Oct. 27, 1964, at a time when the Goldwater campaign lay on the pond of American politics, a lifeless duck. Reagan -- then just an actor -- went on national television to speak for Goldwater and establishing Reagan as a national figure.

But it was a triumph on a narrow stage. In 1964 Reagan spoke the cant of a small political sect; he preached to believers. This year he proselytized, speaking to the anxieties of a nation.

The 1964 speech was negative throughout except for a few paragraphs in which Reagan sought to lionize Goldwater. It was a sustained denunciation of the government in Washington -- "a little intellectual elite in a far-distant capital" -- and the inherited traditions of the New Deal and the Fair Deal. When he departed from those subjects, it was to excoriate the bipartisan internationalism of the postwar era.

Government help for the poor sounded ludicrous in that speech. "If government planning and welfare had the answer . . . shouldn't they be telling us about the decline each year in the number of people needing help?

"But the reverse is true. Each year the need grows greater, the problem grows greater. We were told four years ago 17 million people went to bed hungry each night. Well, that was probably true. They were all on a diet!"

After ridicule Reagan went on to denial: he would, it seemed, happily deny ordinary Americans the government programs on which millions of them had come to depend. Social Security? "Can't we introduce voluntary features that would permit a citizen to do better on his own, to be excused upon presentation of evidence that he had made provisions for the nonearning years?" Farm supports? "Since 1955 the cost of the program has nearly doubled," to no apparent benefit. The government was literally bankrupt, Reagan announced: "We have $15 billion in gold in our Treasury [but] . . . foreign dollar claims are $27.3 billion." Nothing governmental was sacred -- or safe. "Freedom has never been so fragile, so close to slipping from our grasp as it is at this moment," Reagan declared in 1964. "We are at war with the most dangerous enemy that has ever faced mankind in his long climb from the swamp to the stars."

The 1980 Reagan is a close cousin to that 1964 model, but in crucial respects the new model has been overhauled. Negative ridicule is gone. The poor are no longer described as people on a diet -- now they deserve sympathy.

"When those in leadership give us tax increases and tell us we must also do with less, have they thought about those who have always had less -- especially the minorities? . . . Our message will be, we have to move ahead, but we're not going to leave anyone behind."

In 1980, Social Security looks different: "It is essential that the integrity of all aspects of Social Security be preserved."

Government is still "overgrown and overweight," but government power can now be used to constructive ends -- to promote economic expansion provide "a safety net beneath those n society who need help," even protect the the environment.

The "communist master plan" that obsessed the Ronald Reagan of yore was absent from this speech. The candidate deplored a decline in American strength, but made a point of trying to counter any impression that he might be a trigger-happy hawk: "Of all the objectives we seek, first and foremost is the establishment of lasting world peace."

In 1964 Reagan preached against demons that only a fraction of Americans perceived as real. He ridiculed "peace and prosperity," but in 1964 there really was peace and prosperity -- so Lyndon B. Johnson got 62 percent of the vote that year. Now Reagan's demons are the country's as well -- inflation, a flagging economy, the apparent decline of American power and stature in the world.

Instead of picking a fight that his fellow-citizens saw no need to join, as he did in 1964, Reagan has, in 1980, a cause with a broad appeal. The Democrats now in power "say the United States has had its day in the sun; that our nation has passed its zenith. . . .

"My fellow citizens, I utterly reject that view. The American people, the most generous on earth, who created the highest standard of living, are not going to accept the notion that we can only make a better world for others by moving backwards ourselves. . . ."

The question remains whether Reagan's fundamental vision has changed, or whether the times have somehow just caught up with him. There are hints in both the earliest and the latest speeches of his national political career that suggest continuity.

In 1964, Reagan said this: "You and I have a rendezvous with destiny. We will preserve for our children this, the last best hope for man on earth, or we will sentence them to take the last step into a thousand years of darkness."

Thursday night in the Joe Louis Arena here, Reagan said:

"An American president told the generation of the Great Depression that it had a 'rendezvous with destiny.' I believe this generation of Americans today also has a rendezvous with destiny."