Do you remember what it was like before Ronald Reagan brought his special blend of optimism and confidence to Washington? Do you remember when experts regularly called our problems "intractable" and told us that most were probably beyond our comprehension as well as our control? When legislative gridlock was supposed to be permanent?

Every week then, it seemed, some associate of an unsuccessful president was publishing an article championing a single six-year presidential term -- surely the worst idea in its category since the two-term limit was imposed as posthumous vengeance on Franklin D. Roosevelt. It eases the pain of failure when we can believe the fault is institutional rather than individual.

Well, even if you may have forgotten those times, please be assured that at least four prominent and distinguished Americans do remember. The four -- Griffin B. Bell, attorney general, 1977-1979; Herbert Brownell, attorney general, 1953-1957; William E. Simon, secretary of the Treasury, 1974-1977; Cyrus R. Vance, secretary of state, 1977-1980 -- recently co-authored an article in The New York Times, advocating the single six- year presidential term.

They argue that "re-election pressures lie at the heart of our inability to manage complex, long-term national problems." President Ford, for example, "did not press to a conclusion the strategic arms agreements reached at the Vladivostok summit meeting when those agreements were opposed by his challenger in the presidential primaries, Ronald Reagan."

There is a constitutional change needed in the matter of presidential tenure: the repeal of the two-term limit. American voters are smart enough to decide whether they want to consider keeping a preent for more than eight years. But the single six-year term for a president is simply a bad idea whose time has gone.

Just over five years ago, after Jimmy Carter became the first American chief executive to see his job-approval rating drop below the prime interest rate, and the fifth consecutive president to fail to serve a second term, the six-year-term notion had some appeal. But Ronald Reagan's popular stewardship has changed that. In addition to banishing pessimism and expunging the word "intractable" from our public lexicon, Reagan must have singlehandedly made obsolete all those grad-school seminars on the Crippled Modern Presidency or Why Presidents Are Doomed to Fail.

But even without Reagan's impressive job ratings, the six-year term argument is grievously flawed. Implicit in the Bell-Brownell-Simon-Vance argument is the belief that government is too important to be left to politicians and that it's the job of "a modern president to manage government more effectively."

The president leads the nation as well as the government; he embodies the nation as well as he leads it. In 1984, to their detriment, the Democratic presidential candidates seemed to be running for the position as head of the U.S. government. Reagan, instead, ran successfully to be head of the nation that is the United States. A president is much more than a continental city manager or some super federal employee, a GS-100. The successful president is the successful politician who is the successful candidate.

In campaigns, candidates respond to what is on voters' minds -- or they lose. That's what Gerald Ford was doing when he stopped pushing arms control in his 1976 primary contest against Ronald Reagan, and that's precisely what Ronald Reagan was doing in 1984 when, responding to voters' expressed concerns about his own commitment to arms control, he agreed to a summit meeting. And the only reason there is a possibility for tax reform in 1986 is that the Reagan campaign people in early 1984 mistakenly thought the Democrats would be shrewd enough to campaign, that fall, on the Bradley-Gephardt bill.

For those who crave longer presidential campaigns, the six-year term is a windfall, a Pollsters-Media Consultants Full Employment Act. Consider that by this past September, only 10 months after the Republican president's landslide and 38 months before the next presidential election, every GOP candidate seeking to succeed Reagan made sure his presence was felt and observed at the Michigan state convention. The six-year term would mean the 70-month presidential campaign.

The president is right. The two- term presidential limit, in a city where power is truly the perception of power, does diminish the force and effectiveness of any president in his second term. Forget about the six-year proposal. Let's repeal the two-term limit -- now.