Congress was asked yesterday to authorize the immigration of 15,000 refugees languishing in camps and jails in Thailand since escaping from a new "holocaust" in Cambodia.

The appeal came from Leo Cherne, board chairman of the International Rescue Committee and co-chairman of the Citizens Commission on Indochina Refugees, at a Capitol meeting of legislators executive branch officials and private citizens to discuss possible U.S. actions regarding Cambodia.

Cherne said that Cambodians who have left "the worst hell of all" among Indochinese countries are the least helped by present and planned immigration programs because few of them have close family relationships in the United States or previous ties to the U.S. government.

About 9,000 Cambodians are believed to be among the 163,000 refugees reaching here from Indochina since a special program was established early in 1975. Admission of another 25,000 Indochinese was approved by President Carter on March 29, but an implementing paper has not been signed by Attorney General Griffin B. Bell. A spokesman for Bell said the authority should be issued soon, following completion of congressional consultations.

Of the last 10,000 Indochinese admitted to the United States, according to Cherne, only 181 were Cambodians. While 5,800 refugees fled Vietnam by boat in the past month alone, fewer than 40 Cambodians were able to escape on foot in the same period through heavily guarded and mined borders, he said.

Only one in five Cambodians survives the attempt to escape, Cherne estimated.The fact that Cambodians still attempt to flee despite the high odds is additional proof of the oppression and slaughter taking place there, he said, valling Cambodia "the Auschwitz of Asia."

Cherne and other at the Capitol meeting said recent publicity - including an hour-long CBS documentary shown Wednesday night - has raised public consciousness about an unprecedented situation, but without giving a clear indication of actions the United States might take.

Samuel Huntington, a member of the National Security Council staff who accompanied presidential assitant Zvigniew Brzezinski to Peking last month, said Cambodia came up several times in the U.S.-China talks. China has been the principal diplomatic sponsor and military backer of the of the present Cambodian regime.

Other official sources said Brzezinski repeated Carter's publicly expressed concern about "mass killing" and "total suppression of freedoms" in Cambodia, but did not receive any assurance that the Chinese were ready to day anything about it. Chinese officials are reported to have displayed concern about Cambodia's independence, fearing that the U.S. statements and other such international expressions will help Vietnam gain sway over Cambodia.

Among the suggestions made at the Capitol meeting were stepping up of Voice of America broadcasts to Cambodia and enlisting other governments and private insutitutions in learning what has been and is taking place there.