The "Counter Teach-In"-with a slightly modified cast of characters-will take place at 8 p. m. tonight in Sanders Theatre. The chief change will be the absence of the South Vietnamese Ambassador to the U. S., Bui Diem.

Despite the fact that his appearance had been advertised in posters and other publicity for the teach-in, Diem's appointment secretary said yesterday from Washington that the Ambassador's presence at the South Vietnamese National Farmer's Day reception tonight in Washington had been set for months.

Tentative Assurances

Laslo Pasztor '73, however, said yesterday afternoon after he called the Embassy that he had been given "tentative" assurances that Diem would be coming from the time he first made contact with the South Vietnamese two weeks ago up until Wednesday morning, which was the last time he had previously spoken with the South Vietnamese.

Nguyen Hoan, Counselor for Political Affairs at the South Vietnamese Embassy in Washington will replace Diem. Pasztor, organizer of the teach-in, said yesterday that Hoan was the last of four possible speakers that had been originally requested from the South Vietnamese for the teach-in.

Pasztor also stated yesterday that the name of the Thai Ambassador who will speak had previously been announced as Anan Sandering Ham, but was in fact Anand Panyarachun.

According to the Royal Thai Embassy in Ottawa, Canada, Anand Panyarachun is the Royal Thai Ambassador to Canada and the Acting Permanent Representative of Thailand to the U. N.

'No Such Person'

The information officer at the Thai Embassy in Canada said that "there is no such person as Anan Sandering Ham." He did note, however, that the building in which the Thai Embassy is named the Sanderingham Building.

The rest of the speakers, Dolph Droge, White House Vietnam advisor; I Milton Sacks, professor of Government at Brandeis; and Dan Teodoru will appear as advertised.

Despite the change in speakers, radical groups at Harvard have decided to go ahead with actions already planned for the teach-in.

'Heroic Struggle'

Harvard-Radcliffe SDS and the University Action Group, a group of radical faculty members and graduate students generally allied with SDS, will try to prevent the speeches with loud applause for "the heroic struggle of the Vietnamese people."

However, SDS-UAG spokesmen emphasized that the final actions taken would depend upon the situation at the 'counter-teach-in' itself. Both SDS-UAG and the Radcliffe-Harvard Liberation Al-liance have called for supporters of anti-war actions to meet at Sanders at 7 p. m. to decide on a course of action.

Members of the Liberation Alliance reaffirmed last night their plans to "turn the teach-in into an anti-war rally" by clapping, heckling, carrying Vietcong flags and other actions." The group as a whole has not voted to clap the speeches down.

Amy Brodkey '71, a member of the RHLA, said that she didn't expect the group to take any actions which would actually prevent speeches, particularly in a way that might be interpreted as a violation of the University Resolution on Rights and Responsibilities. But, she said, "clearly the administration will interpret these rules the way they want to."

Dean Epps said yesterday that clapping or heckling which led to the cancellation of a speech might be prosecuted in the CRR. But, he added that it was a question of degree, saying "it depends if the speaker can be heard."

All antiwar groups planning actions have ruled out any attempts to block the speakers physically-by picketing outside or demonstrating inside-along with any form of physical violence.

Marshalls?