In the Roosevelt Room of the White House, Mission Control on election night, one of the four television sets suddenly blared forth a stunning CBS projection -- Republicans appeared to be losing 34 seats in the House -- and it could be even higher.

"That's crap," said a White House aide. But other presidential advisers were immediately apprehensive.

It was just 8 p.m. Most of the election night was still to come. The president and his guests were eating off TV trays on the second floor of his residence as his advisers monitored results from their Mission Control.

Throughout a bizarre evening they would be introduced to winners who would lose and losers who would win as the nation's voters treated many of the nation's politicians and pundits to a November surprise.

"We were really taken on a roller coaster ride," said one presidential aide, who was still unsteady the morning after. By then the results were clearly not good--and in fact, not yet totally clear. But as the Reagan aide said:

"For a while all we were hearing was that it was going to be much worse."

In Binyon's Restaurant in downtown Chicago, Democrat Adlai Stevenson III had called his campaign disciples together for a last supper. The pollsters had offered him a smorgasbord of final predictions: the worst news was that he would lose his bid for the governorship to incumbent Republican James R. Thompson by 26 percent; the best was that he would lose by only 15.

It was 7 p.m. and the polls were just closing in Illinois. An aide said that he expected that the television networks would be calling the results by 7:15 p.m. "We'd better hurry and have the first round of cocktails," he advised soberly.

In Austin, Texas Gov. Bill. Clements was feeling no pangs. He had spent big, campaigned hard, and finished strong. His pollster, V. Lance Tarrance, had charted it on election eve as 52 or 53 for Clements, which, while not a Texas-sized victory margin, was at least comfortable.

Republican Rep. Jack Fields of Houston telephoned Tarrance in midday to say that union precincts were voting about twice as heavily as they had anticipated. And a Democratic pal from Austin had called to say that there was a rainstorm in east Texas, but blacks still seemed to be voting in greater proportions than whites, which is not the way it usually happens. But probably those were aberrations.

Back in the Roosevelt Room, the president's aides were monitoring the three major networks by using earphones, discovering one by one that most of the moderate eastern Republicans were locked in tight races.

From a fourth, larger TV set, where the audio was turned up for all to hear, came some good news and bad news from CBS.

Rep. John P. Hiler (R-Ind.) was gone, the network projected early. This loyalest of the Reaganauts was going down in defeat. But Rep. H. Joel Deckard (R-Ind.) seemed destined to win reelection after all, despite a close scare, the network said.

The ballroom of the Sheraton Centre Hotel in midtown Manhattan was alive with the theme from "Fame." Liberal Democrat Mario Cuomo's people had just announced that ABC and CBS have projected Cuomo the winner over conservative supply-side Republican Lewis Lehrman, in this gubernatorial race that all the nation has been watching as a referendum on Reaganomics. A Cuomo victory was, of course, no surprise; the final newspaper polls have all shown him ahead by nine or 10 points.

So they struck up the band. Cuomo would be down shortly to give his victory speech, they said.

White House chief of staff James A. Baker III was walking back to the Roosevelt Room after having watched the early returns upstairs in the mansion with the president and a few of his intimates. He had planned to brief the press early, by 9 p.m., but the news was not good, and so he was in no hurry to meet the press.

Meanwhile, results poured forth from the television sets. In Texas, Republican incumbent Clements was being beaten soundly. In Illinois, Republican incumbent Thompson was having far greater trouble with Stevenson than even Stevenson expected. Some of the moderate Republicans in the Senate had won, after all. The House races were looking a little better for Republicans, but they were still far from good.

Baker decided it was time to face the klieg lights. He had decided to emphasize the Senate, where the Republicans have won a stay of execution, if not a mandate to stay the course. " . . . the first time since 1928 that Republicans will have held the Senate for two consecutive Congresses."

Shortly before midnight, the nation was treated to a rollback of impressive proportions. In Texas, Clements was indeed down to a surprising defeat. The black vote was large--and had gone overwhelmingly for Democrat Mark White.

Rep. Mickey Leland of Houston said a single black precinct in his city had reached the quota of Democratic votes projected for it by the Democrats by 10 a.m.

A huge voter turnout had done Clements in, Republican and Democratic strategists later agreed. A Democratic get-out-the-vote drive had 100,000 volunteers calling 125 people each on Election Day to get them to the polls. And in those precincts where the early turnout had been reported light, the Democratic volunteers had proved able to rev up their phone banks and boost the late turnout dramatically.

But in New York, Cuomo, who had unanimously been declared the next governor by the networks, was suddenly undeclared: he was actually trailing Lehrman by the barest of margins. Lehrman, who spent more than $7 million of his own money in his own cause, had poured $1 million into a last-minute flood of targeted direct mail. He tried to convince Italian-Americans to vote their conservative Republican political beliefs and not their heritage. He sent separate, differently worded, appeals to Jewish voters urging them to remember Lehrman's strong family traditions.

It was after midnight when Cuomo finally won the race after all--and then only by a hair's breadth. Lehrman first said he would demand a recount. But instead, the afternoon after, he graciously conceded defeat in a campaign in which he had spent so much of his own money to come so close. He said he would be keeping his campaign staff together--for purposes as yet undisclosed.

And in Illinois, Stevenson finished his election night dinner a far stronger candidate than he was when he sat down: his race was too close to call.

This was partly because of his last-minute ads that stressed the reasons why voters had earlier been unhappy with Thompson as governor (because he had accepted some gifts, because of high unemployment in the state).

It was also because a key portion of the ballots in Cook County were suddenly too wet to call; humidity had made the punch card ballots so damp they could not be processed by the automatic counters, and so the politicians were locked in the suspended animation of what the elder politicians of that famed machine county explained was a drying-out process.

It began to seem as if, with the election over, the get-out-the-vote efforts were still under way. Thompson held a thin 33,000-vote lead in the incomplete returns. But yesterday, in the city of Chicago itself, there was still another foulup.

Twenty percent of the city's precincts had been lost in the electronic computer tallying, and the city elections board chief had sent the proofreaders home at midnight. They were to resume counting today, with the city elections board chairman, Michael A. Lavelle, noting in an interview that it was still possible that the city's pro-Stevenson wards might yet put the Democrat into the governorship.

In Indiana, it turned out, Hiler was brought back to political life with a narrow victory--and Deckard was defeated.

And nationally, the networks were scaling back from that high CBS projection of Republican House losses, agreeing that it was probably about 20, after all.

It was well after 1:30 a.m. Wednesday when the men and women of the Reagan White House filed out of the Roosevelt Room Mission Control, where they had just spent most of the night lost in space. They would awaken to find things a bit worse, the morning after. The Republican losses in the House now totaled about two dozen.