A "new era" was widely proclaimed when Ronald Reagan won the presidency six months ago. The stumbling of the administration since then heaps doubt on the theory that the Republicans have irreversibly become the majority party.

But a cluster of recent events defines with precision one change that indubitably has occurred. The Watergate spirit is dead.

By Watergate spirit, I mean a pervasive belief that the serious troubles in this country flow from a concentration of power at the top. Wrongdoing supposedly flourishes as a result, and its supreme expression is the coverup. It follows that what the country most needs is a change of moral atmosphere -- an uprooting of corruption and of old-boy networks, and a filling of the void by air, sun and enlightenment.

Established authorities in all headquarters were put on the defensive by the Watergate spirit. The initiative passed to confident prosecutors and gung-ho investigators in the press and television.

The recent reversal in national spirit finds a dramatic example in the case of the Pulitzer Prize returned by The Washington Post after it became known the award-winning story was a fraud. So much has been said on the subject, some of it by those with scores to settle, that further comment seems almost abusive. But the opening line of the ombudsman's report bears repetition as an apt description of the larger significance of what happened. The event, Bill Green wrote, "humiliated The Washington Post -- proud house of Watergate investigations."

On the other side of the same coin was the decision by President Reagan to pardon two former top officials of the FBI who were convicted by a jury of conspiracy to stage illegal break-ins in 1972 and 1973. The pardon was issued by the president before the appeals process had been exhausted, and without the normal investigation by the Justice Department. By Watergate standards, there should have been a burst of outraged criticism, with alarms of cover-up and fix-ringing all over the country.

But the one comment in that vein rang false. John Nields, the attorney who originally prosecuted the case, said he was "extremely distressed" because the pardon would "send out a terrible signal -- that the government can violate the Constitution and then forgive itself."

If that were true, then a case so likely to have ended in a pardon should not have been prosecuted in the first place. But, of course, it is not true. The two FBI officials who broke the law opportunists, confident they would earn brownie points from their superiors. Instead, they suffered ignominy, a harrowing trial and heavy financial penalties. No one is likely to follow that lead again soon. The Watergate lesson has been taught. It does not need to be rammed home.

A more important, perhaps -- through still largely unnoticed -- development is an evolution inside the Democratic Party and the House of Representatives. In 1974 and 1976, 118 freshmen Democrats were elected to the House. Those Watergate classes initiated a spate of reform that opened up procedures and sapped the principle of seniority. To no small degree, the inability of Congress to deliver for Jimmy Carter reflected the balkiness of the Watergate classes.

But 1981 has witnessed an assertion of self-discipline by the House Democrats. They have surfaced a statement of economic principles, and a budget, and a tax program. Four junior members -- Richard Gephardt, elected in 1976 in St. Louis; Norman Mineta, elected in 1974 from San Jose, Calif.; Leon Panetta, elected in 1976 from Monterey, Calif., and Tim Wirth, elected in 1974 from Denver -- all played leading roles in formulating the joint program. Their performance traces a striking transition from purist reform to the building of majorities.

Gephardt acknowledged the point in an interview the other day. "Watergate is now over," he said. "We're not looking for more reforms. We don't think opening up hearings and attacking the leadership is what it's all about. We understand that we have to make things work. We have to help run the country."

The end of Watergate, to be sure, carries certain risks. There remains a danger of arbitrary state interference in the private lives of individuals. Cover-ups are not over and done.

But the fact is that noble intentions -- whether moral, as in the case of Jimmy Carter, or patriotic, in the case of President Reagan -- are not enough. A sense of responsibility also counts. The system must be made to work, and that means, on the part of all of us, a recognition that some of our best impulses may have bad outcomes.