After months of often hectic bargaining, NBC and the Soviet organizing committee for the 1980 Moscow Olympics signed agreements last night in Moscow that give the network exclusive rights to broadcast the games in the United States for a price expected to exceed $70 million.

Hearty handshakes and champagne at the signing ceremony could not overcome the heated atmosphere that had marked the negotiations. In congratulating NBC on its success, Ignati T. Novikov, president of the Soviet committee twice referred to it as ABC - the competing network which until the fianl hours held out hope that it might win the contract.

In New York, the mood at NBC - which has been suffering a poor ratings year this season - was ebullient, particularly at defeating ABC's last-minute bid for the Soviet rights.

Said one NBC spokesman: "Roone Arledge is tasting the agony of defeat."

Meanwhile, New York officials of the Soviet-American Trade company (SATRA) sent letters to the president of NBC Television and parent corporation RCA Inc., threatening to sue both for damages and violation of anti-trust statutes. SATRA announced in late December that it had signed its own agreement with the Soviets for exclusive TV rights to the 1980 Olympic games.

SATRA Chairman Ara Oztemel said yesterday his firm was given no official indication that the agreement had been nullified. "This is a new experience for us, after 25 years of dealing with the Soviet Union," Oztemel said. "Never before have we had a signed and sealed agreement be totally ignored."

As explained by Soviet officials in Moscow, the contracts with NBC consist of two parts: the right to air the games in the U.S. for which the network will pay $35 million - of which a third goes to the International Olympic Committee - and a separate agreement for "technical cooperation" that the Russians say should top $35 million once the costs of equipment and services are totalled.

Network sources indicated that the final outlay for rights could easily reach $80 million, which is still somewhat less than the $100 million the Soviets were once thought to be asking.

NBC therefore will be paying out about three times as much as ABC did for the rights to the Montreal Olympic last summer. At a press conference in the organizing committee's headquarters, Soviet spokesmen defended the high price as reasonable in view of the growing worldwide audience for the Olympic games, the sophistication and expense of broadcast equipment and the added problems of televising great distance as well as in color.

Whatever the sum that NBC and other foreign company pay for tetlevision rights, said Vitaly Smirnov, the Soviet committee's executive vice president, "will only in part" cover the outlay Moscow is making for broadcast facilities.

In notably forthcoming remarks on the complex negotiations - little was revealed previously - the Soviets said yesterday that NBC had won the bidding because its terms, in price and timing of payment, proved to be the best, although the IOC made allowances for ABC's greater renown as a sports broadcaster.

IOC approval of the agreement is required and was voiced last night by Monique Berliox, the committee's financial secretary. She also said that the committee was satisfied that conditions for "all participants in the bargaining were equal" - and assurance that the networks had openly doubted during an earlier phase of the talks.

At issue then was the role of the SATRA corporation, a New York firm specializing in Soviet-American trade. SATRA showed up unexpectedly during a key Moscow meeting in December. When the networks - which at that point also included CBS - walked out, the company signed a document which it boldly portrayed as an agreement to televise the Olympics in the U.S.

Some network officials maintained that SATRA had been brought in by the Soviets to further complicate the talks and drive up the price of the contracts. Soviet spokesmen disputed those assertions last night, saying that the exchange with SATRA had simply [WORD ILLEGIBLE] that was signed because all the other American contenders had broken off talks.

Soon thereafter, the Russians said, it was decided in Moscow and by the IOC that CATRA would not be a suitable oultet for broadcasting the games because of its lack of experience in that area. SATRA officials watched glumbly from the sidelines last night in Moscow.

But in New York SATRA president Oztemel claimed his company had already put together a "fourth network" of TV stations that would carry the Olympics and pay SATRA for supplying the coverage.

Oztemel declined to reveal how much money SATRA had agreed to pay the Soviets under its agreement but said it was "considerably less" than the $80 million to be paid by NBC.

An NBC spokesman said the letters from SATRA had been turned over to company attorneys and would not comment except to say, "We believe we acted lawfully and properly" in negotiating the agreement with the Soviet Olympic Organizing Committee.

Oztemel said he was aware of news reports that NBC was negotiating with the Soviets but said he had received no official notice that SATRA's already signed agreement would not be honored.

Only two days ago we received a confirmed invitation from the International Olympics Committee asking us to meet with them in Luzanne to discuss their approval of our presence at the Olympics," Oztemel said.

"We had no reason to believe anything was wrong. We were led down a misguided path. It surprises me very much. I'm angry. I'm not angry at the Soviet Union or its people in general. In 25 years we really haven't had this kind of problem before."

As the Soviets presented the picture last night, the main stumbling block in December was network interest in a pool arrangement, which the Russians firmly resisted on grounds that additional technical problems would result. The differences led to the breakdown of talks, the Soviets claim, rather than American refusal to pay the money then being demanded.

Once the pool idea finally collapsed several weeks ago when CBS said ti was definitely not interested in televising the games, talks again began with NBC and ABC. NBC president Robert Howard and a small team of aides arrived in Moscow last Wednesday for intensive discussions while ABC's representatives arrived over the weekend.

Part of the continuing trouble in the negotiations appears to have been misunderstanding. For instance, NBC, which had no Russian speakers on its team and used Soviet-supplied translators, ended a bargaining session Sunday by telephoning correspondents here with news that a deal had been struck.

But the Russians said matters were still in the "letter of intention" stage. They saw no contradiction in continuing talks with ABC until a final decision was made. That led to confusion Monday when NBC was proudly claiming success while the Russians remained coy.

NBC officials were reluctant to discuss the negotiations yesterday, saying that a network press conference would be held in New York on Friday. However they did indicate that no pledges had been made to the Russians about the contents of Olympic programming aside from sporting events - A contentious issue, given well-known Russian sensitivities on how their country is portrayed abroad.

ABC publicly conceded defeat yesterday with a statement from its president, Frederick S. Pierce. Pierce said the network had "returned to Moscow with a fully competitive bid, seeking further clarification of potentially burdensome conditions . . ." But NBC got the contract before ABC got the clarification.

The statement also said: "We deeply regret that the American viewing public will be deprived of the experience and expertise gained by ABC Sports in televising six of the last seven Olympic games."

The terms of the "technical agreement" remains to be fully explained. As the Soviets evidently see it Americans and othe foreigners will begin supplying equipment and expertise intended to defray the costs of transmission during the games. NBC also expects that its agreement will enable it to provide the flexibility and variety of coverage that the Soviets might not be capable of alone.

In any case, NBC's money will start flowing to the Russians very soon. How much could eventually flow back to the network, through the sale of advertising time on the games, it unclear.

Broadcasting executives in New York were speculating yesterday that with $80 million invested in the rights alone, it will be all but impossible for NBC to make a profit on the deal.

At most, one industry source estimated, the network will have a total of 700 minutes of commercial time to sell, and even at $125,000 a minute - very high for a sports event - the network would take in only about $87 million, hardly enough to show a profit since production costs for the games could go as high as $50 million in additional expenses.

ABC charged about $82,000 a minute for commercial time during the 1976 Olympic Games from Montreal, sources said, and showed only a small profit - in network television terms - from the games. The network lost money on its coverage of the 1972 Munich Olympics, sources said.

ABC paid Montreal $25 million for the 1976 games and $13.5 million for the Munich games.

NBC would not comment on how much money it intends to charge advertisers for commercial time on the 1980 Olympic games, but a spokesman said such figures will be made public later.