Setting aside previous predictions, analyses and explanations -- no easy trick -- the question now before the nation's pollsters and pundits is, what happened?

The answers are -- naturally -- still tentative. If this were China, 1980 might be called the Year of the Roller Coaster. It was a rocky morning-after for a lot of the experts yesterday, but they did have some more or less plausible explanatory theories, too.

Several factors -- some new to 1980, others as old as primary elections -- help explain not only yesterday's surprising results in New York and Connecticut, but also earlier surprises in the Iowa caucuses and primaries in New Hampshire, Massachusetts, Vermont and elsewhere.

One factor at work this year, numerous pollsters and political analysts agreed yesterday, was that voters' negative impulses have been directed not only at the sitting president -- a normal phenomenon -- but also at various challengers. Thus John B. Connally, George Bush and especially Edward M. Kennedy have all been the victims of voters' negative feelings this year.

On Tuesday, voters in a sense reverted to traditional form, using their negative votes to punish Jimmy Carter, the sitting president, instead of his challengers. Most analysts interviewed yesterday said Carter had become the central issue in the New York and Connecticut primaries, a departure from all the earlier contests this year.

The inclination to use one's vote to vent frustration produces both last-minute choices and also decisions not to vote at all. (In New York Tuesday, 26 percent of the registered Democrats turned out to vote, a small number.) Unmoved by enthusiasms for a candidate, voters are often debating now whether they're angry enough to turn out against someone.

According to a number of those interviewed yesterday, willingness to vote against President Carter is suddenly and quite dramatically increasing. The long-term significance of this shift remains to be seen, but it is significant.

Gary Hoggard, a pollster who has been sampling opinion in a number of blue-collar congressional districts in the Northeast and Midwest said yesterday his figures show a sudden sharp increase in personal economic anxiety between mid-February and mid-March. In February no more than 3 percent of voters he polled said they thought their jobs might be in jeopardy because of national economic conditions. This month that number jumped to around 20 percent, Hoggard said.

Hoggard speculated -- and other pollsters agreed -- that the 18 percent inflation, reinforced by this week's election-day announcement that it has remained at this staggering level for two months, has crystallized personal anxieties about economic conditions.

Robert Teeter, a pollster working for Bush, said he thought politicians had underestimated the impact of popular attitudes of interest rates, now also nearing 20 percent. The view that inflation is now an old and familiar problem to Americans is inadequate today's suddenly worsened conditions, several analysts said.

Hoggard said if his analysis of the shifting impact of economic conditions on voter attitudes is correct, Carter will be in grave trouble in the April 22 Pennsylvania primary, which now looks like a crucial encounter for the president and Kennedy.

But such predictions are of limited value, not least because of another factor that seems unusual this year, and which has colored this year's primary results, according to many experts.

As Teeter put it, "We've had one helluva lot of news," both in the last few months, and just in the last week. "The press is giving voters huge quantities of information," Teeter said, "which doesn't leave them much long-term perspective."

A senior official in the Carter campaign agreed, adding that whatever benefit the president got from his big win in Llinois last week was wiped out in a few days by economic developments and particularly the flap over the deposed shah of Iran and his departure for Egypt.

Several of those interviewed said they thought the Iran issue -- which revived Carter's fortunes dramatically last fall and winter -- may now be turning against Carter.Louis Harris said his poll of New York voters just before Tuesday's balloting showed that New York Democrats, by a 51-to-30 margin, thought the president's handling of the hostages crisis had been "a failure."

The intense sequence of big events that has already made his campaign year so unpredictable is still continuing, presumably, so predictions remain risky.

Several pollsters and analysts said yesterday that 1980's primaries really weren't so unusual. "Primaries are always volatile," Teeter said. Primary elections have always provided an occasion "to let off steam," Harris added.

The question that seems to fascinate these experts is whether something has now happened in the electorate to focus attention -- and steam -- primarily on a single target, Jimmy Carter.