A senior Soviet commentator today described the Republican convention that nominated Ronald Reagan for president as a television-dominated carnival that adopted a platform of irreconcilable differences.

Vitali Kobysh, writing from Detroit for the influential weekly Literary Gazette, acidly declared, however, that Reagan and running mate George Bush "could well become the next White House tenants as a direct result of the crushing failures of J. Carter in every respect."

The commentator, a senior aide in the Communist Party Central Committee's information department, drew the line well short of outright condemnation of Reagan.

"You could not call [his advisers] irresponsible or not serious," Kobysh wrote. "It's hard to image that once in power, shouldering the burdens of government responsibility, they would try to put into practice the platform planks set out in Detroit."

In recent weeks, as Reagan's nomination became a foregone conclusion and his standing in the polls rose, the Soviets have backed off longtime harsh criticism of him as cold warrior. But Kobysh, whose views are considered to represent some segments of the ruling apparatus, said the Republican platform is "trying to mix the unmixable" by proposing cures of inflation, sagging productivity, unemployment, and increase military spending at the same time.

Meanwhile, the Communist Party paper Pravda said the Republicans "are placing stakes on a new spirit of anti-Sovietism and firing themselves up with calls for a buildup of military preparations in an attempt to defeat the Democrats."

Asserting that the Detroit convention was an empty show dominated by the TV networks, Kobysh wrote, "It is hard to tell where is show and where is policy, where is TV and where is real life."

He said Americans are suffering a national crisis of confidence. "Something seems to have broken inside many of them, they have lost their self-confidence, they are not so sure about the future of their country." t

Kobysh continued the harsh criticism of President Carter's government, declaring, "from its first weeks in power, when it pompously announced the march for human rights, until the very last months, when inglorious military-political adventures took place, like the [rescue operation] buried in the Iranian desert, the present administration has been confusing reality with TV all the time."