The Soviet Union expanded its allegations of American subversion in Afghanistan today in a continuing effort to blunt world criticism of the Soviet military intervention there.

An authoritative article in the government newspaper Izvestia said, "The U.S. Central Intelligence Agency is directly involved in training Afghan rebels in camps in Pakistan and maintaining contacts with counterrevolutionaries and reactionaries in Afghanistan itself."

The paper claimed that CIA agents under cover of "the antidrug board and the American 'Asian Fund' operate in the area of the Afghan-Pakistan frontier."

Izvestia apparently meant the U.S. Drug Enforcement Administration (DEA), which has investigators in the South Asia region as part of the federal government's worldwide narcotics traffic suppression efforts. The "Asia Fund" could not be specifically identified but may be a Soviet reference to the Asia Foundation, a private American assistance organization.

The State Department refused to comment on the Soviet charges, but one official said a DEA agent is permanently assigned to the embassy in Afghanistan. The agent, however, was out of the country on vacation at the time of the Soviet incursion, according to the official.

Under the authorship of Mikhail Mikhailov, regarded here as an authoritative voice, reflecting leadership views, Izvestia expanded earlier official accusations to include Britain and Pakistan, along with China and Egypt, in the alleged subversion effort undertaken by Washington in Afghanistan.

"Pakistan's anti-Afghan course had the support of the U.S. and Britain," the paper said "and was decisively the result of instigations on the part of these countries, China, Egypt, and some others."

Two days ago, the Communist Party paper Pravda hinted, strongly that Pakistan was involved directly in the alleged subversion plot. By naming Islamabad in today's account, the Soviets appear to have written off any early easing of their already strained relations with the Pakistanis, who have strongly backed China in a series of Soviet-Chinese confrontations. Islamabad, like Tehran and other Moslem capitals, has sharply denounced the Soviet military incursion, which Washington estimates at between 30,000 and 40,000 with another 12,000 or so ready to cross the border.

Meanwhile, the official Soviet Tass agency reported a telegram of thanks to Soviet leader Leonid Brezhnev from Babrak Karmal, who came to power in Kabul Thursday in the Soviet-backed coup.

Babrak, a staunchy pro-Moscow communist who was pursed from Kabul leadership last year by the man he overthrew, Hafizullah Amin, told Brezhnev he is "convinced that with the fraternal assistance and undiminishing cooperation" of the Soviets, "we shall win and overcome all difficulties we inherited from the past."

Soviet media have avoided describing the insurgents opposed to Kabul's Marxist government as Moslems in an apparent attempt to improve relations with other Moslem countries. In describing the angry rally by Afghan exiles at the Soviet Embassy in Tehran today, Tass simply called them "hooligans who refused to disclose their names" and said they were "hostile to the Afghan revolution."