Waiting on the runway for a private plane to be repaired while he was campaigning for Republican candidates in the fall of 1968, Ronald Reagan lapsed into a discussion of the financial problems of Social Security.

After listening to various Reagan suggestions for reforms, a reporter asked the then-governor of California whether he planned to discuss them in future campaigns. Reagan looked at the reporter incredulously and shook his head.

"You can't run against Social Security," he said. "Barry [Goldwater] proved that."

This was Reagan the Politician talking, a man who pays as much attention to survey data as Jimmy Carter, the man who in this campaign has changed his position from "no" to "yes" on the Chrysler bailout, from "no" to "maybe" to "yes" on federal aid for New York City and from "no" to "probably yes" on price supports for farmers. Throughout the fall campaign, this Reagan has muted much of his conservative rhetoric in an effort to reposition himself as a born-again New Dealer sympathetic to the plight of blue-collar workers pinched by unemployment and inflation.

But there is another Reagan running for president this fall, Reagan the True Believer. This Reagan is a conservative who has rejected repeated recommendations from his advisers to abandon his support for an across-the-board 30 percent tax cut over three years that has been described by his own running mate as "voodoo economics." This Reagan said again last week, in an interview, that he still wants to abandon the new departments of Energy and Education.

Reagan's efforts to portray himself as a friend of the unions, an environmentalist and a supporter of a host of government programs have been ridiculed by President Carter and members of his cabinet. Reagan's fall campaign strategy has left liberals crying "foul" and conservatives asking whether their champion has become a two-timer.

But voters must contend with both Reagans as they watch the last days of the campaign play out. Reagan has been described as "a man of parts," and there has always been a distinction between candidate Reagan in the primaries and candidate Reagan in the general election. In the primaries, the candidate is the figure familiar from the conservative banquet circuit -- confrontational rhetoric, militant anti-communism and gibes at government that identify with business audiences.

This is the Reagan who tried to outflank Nixon on the right in his short southern campaign of 1968 and it is the Reagan who battered Ford on the Panama Canal in the nearly successful campaign of 1976. It is the Reagan who emphasized his opposition to gun control and abortion in New Hampshire during the primary campaign this year.

And then there is the general election Reagan. In 1966, Reagan relegated members of the John Birch Society, then an important element in California, to the task of canvassing each other and said that any Bircher who supported him was "buying my philosophy; I'm not buying theirs." His issues were student disorders, then a cutting issue among working-class Democrats who had not sent their kids to college to blow up buildings, plus inflation and the tax increases under the administration of then governor Edmund G. (Pat) Brown.

In 1970, when he ran for reelection, Reagan did so as an incumbent who had given the state good government, and he took credit for the property tax relief passed by the Democratic legislature under the imprimatur of his opponent.

In California, Reagan was the darling of conservatives in his first months in office. But when he proposed a major tax increase that sharply raised the rates on banks and businesses, the right wing denounced him and commissioned an anti-Reagan book called, "Here's the Rest of Him."

This fall there are dozens of instances where Reagan uses milder language or more politically acceptable examples to make a familiar point. For years, Reagan has been telling business audiences about the evils of the regulations in agencies that grew out of the New Deal. He now promises working class crowds a "message of hope" that preserves the New Deal legacy, including government intervention to provide jobs.

Sometimes the jobs he promises are in the form of specific programs, as he did in New York recently when he told construction workers he supported huge federally financed highway programs such as New York's controversial Westway project, a position consistent for a man who presided over a major state highway building program in California.

Though his advisers say he remains committed to turning welfare programs back to the states, Reagan rarely mentions it in his speeches these days. And instead of his once-harsh attacks on the Occupational Safety and Health Administration, Reagan said in an interview last week that he would like OSHA to become "kind of a helpful research operation" that would ask businesses what their safety problems were and then devise a plan for helping them solve those problems.

At the same time, his conservative rhetoric rings loudly, as it did this week in Ohio when he called for the Clean Air Act to be rewritten. But such attacks are couched in the language of jobs and productivity, a message that Reagan's advisers believe will gain him the support of many normally Democratic workers. The Reppublican nominee is attempting to give a selective version of his old anti-New Deal messagae to an audience that favors the more tangible offerings of a strong central government -- Social Security, unemployment and medical benefits and protectionist trade policies.

The reincarnation of Reagan as a New Dealer in part reflects survey data presented to Reagan in the autumn of 1979 that showed Carter uncommonly weak among blue-collar industrial workers who were a linchpin of the old New Deal coalition. The data also showed Sen. Edward M. Kennedy (D-Mass.) with strength in this constituency, suggesting that Reagan's general election strategy would have to depend upon the identity of the Democratic nominee.

Reagan's bland announcement speech last November left plenty of running room in either direction, combining as it did his standard antigovernment rhetoric with a story Reagan told, with a tear in his eye, about how his father had been fired on Christmas Eve during the Depression.

Carter quickly moved out in front of Kennedy, and Reagan told the same story again, with more tears, as he appealed for working-class votes during the primaries in the crossover states of Illinois and Wisconsin.

Although this "repositioning" was taking place throughout the year, it was to reach full flower in the general election campaign.

Late in August, however, Reagan almost blew the entire strategy by telling conservative audiences at long-scheduled forums what they wanted to hear.

In Dallas, before fundamentalist ministers, Reagan was sympathetic to teaching the biblical theory of creation along with the theory of evolution. In Los Angeles, he proved unwilling to totally abandon Taiwan and infuriated the government of the People's Republic of China. In Chicago, before the Veterans of Foreign Wars, Reagan called the Vietnam war "a noble cause."

These developments diverted the campaign from economic issues and horrified some of Reagan's more centrist advisers. The comments also produced a sharp drop for the candidate in his own polls, and it was this decline that impressed itself upon Reagan.

"The governor realized that he couldn't develop his issues if he became the issue," said one strategist. And ever since Labor Day, Redagan has been sticking to what his data tell him are his opponent's weak points.

This strategy does not sit particularly well with either the handful of Republicans on the party's liberal wing nor with the ultraconservatives who have been largely shut out from key campaign positions. The Republican liberals are worried that Reagan will put into practice the old conservative agenda when he becomes president. The conservatives are concerned that Reagan's conservatism may prove as ephemeral on many issues as it did when he was governor of California.

These doubts on the right are deepened by the emergence in the Reagan campaign of pragmatists who were close to former president Ford -- en like Stu Spencer, William Timmons and James A. Baker III. The pragmatists are delighted with Reagan's present course and some think they have been influential in keeping him to it.

"I think it's what he should be doing and I don't see it as an abandonment of principle," Baker said this week.

There has never been much doubt within the Reagan organization that he would campaign, if he could as a born-again New Dealer, for the politician in him -- and it is the politician who predominates -- tells him this is the best way to win the election. What that politician in him would tell Reagan as president remains to be determined by events.