The Soviet Union, after a guarded delay to test world opinion, has reacted with anger and alarm to President Carter's suggested boycott of the 1980 Moscow Olympic in reprisal for the invasion of Afghanistan.

The official media now has labeled the administration's suggestion "political blackmail," aimed at "undermining international detente and seriously aggravating Soviet relations," as the newspaper Soviet Sport declared in the first official acknowledgment of the question.

Meanwhile, sources here say they believe Soviet sports officials have recently dropped veiled hints to foreign officials that a boycott by the United States of the Moscow Olympics could open the door to retaliatory boycotts of the 1984 Summer Olympic Games in Los Angeles. These reports could not be independently confirmed.

However, a senior Soviet Olympic official said in an interview today that he feels "it's impossible to exclude the Moscow games between the Lake Placid and Los Angeles games." But Vsevolod Sovva, information chief at the olympic press center, declined to speculate about any future participation possibilities, calling such questions hypothetical.

He left no room for doubt, however, as to where the Soviets stand on a possible boycott: "The Olympics and a boycott are incompatible. Any such boycott, and the Olympics would cease to exist. The Olympic charter excludes such discrimination, or any connection between the games and political purposes."

As for Afghanistan, that situation has been more than adequately explained by President Leonid Brezhnev, Sovva said, and it has no connection to the Olympics. "It is groundless trying to connect unconnected things," he said.

Brezhnev has said the Soviet military intervention saw in response to pleas for assistance from the Marxist Kabul government to defeat interal subversion fomented by the United States and China.

Sovva said he hoped American talk of a boycott was an "irritation" that would fade. "The doors of Moscow are open and we are for the survival of the Olympics, not destruction. If someone else wants to destroy the games, that's their business."

He echoed the view of Lord Killanin, head of the International Olympic Committee, saying "They [the Olympics] shouldn't be used for malicious political purposes. We keep to this. To hold or not to hold the games is the business of the IOC and the national Olympic committees and along this line, no one has said anything about not desiring to participate."

As for Saudi Arabia, which last week declared it would boycott and called as well for an Islamic boycott, Sovva said the Saudia had informed Moscow last October they were not interested in participating. "It was for their own reasons," he said. "I think it is impossible to twice reject proposals of marriage. One time is enough."

For the Soviets, even the slightest hint of a boycott by their principal capitalist competitors has had a noticeable dampening effect after five years of intense preparation to showcase the Soviet system to the world.

A senior architect for the huge press center, a marbled building near the Foreign Ministry in central Moscow, expressed some of this during a tour of the nearly finished building. "As an architect, I would like to see the building work," he murmured. "Much would be ruined, but not only for me, for the sportsmen as well."

The center will accommodate several thousand foreign and Soviet reporters and about 1,000 Soviet citizens trained in English and other languages to help foreigners.

Moscow has spent unknown hundreds of millions rubles and hard currency here and in Leningrad, Kiev, Tallinn and Minsk, the other venues, to refurbish and enlarge older stadiums, build new ones, put up an Olympic village to house approximately 8,000 athletes and team officials and dress up their cities for an estimated 200,000 foreign tourists.

Sovva said about 1.5 million tickets already have been sold to foreign travel agencies handling the bookings for tourists and he expects the rest to go soon.

A complication has arisen, however, in Washington's cutback of New York-Moscow Aeroflot flights in reprisal for the Soviet invasion. Sovva said the reducation has already meant difficulties for Soviet Olympic officials headed to the Lake Placid Winter Olympics next month and travel plans for some of them may have been postponed. o

Otherwise, he said, aided by a generally mild winter so far, preparations are speeding ahead. The major question mark seems to be the huge indoor swimming stadium on Prospekt Mira north of the Kremlin. This swaybacked, circular facility, Europe's largest at 45,000 capacity, is architecturally the most ambitious of the new buildings and the one the Soviets have had the most serious delays on. But Sovva said it will be completed in time for the July 19 opening ceremonies.

In the context of Soviet life, where projects invariably fall behind schedule or frequently are never completed at all, the pre-Olympic preparations are remarkable.