After issuing an emotional appeal to President Carter not to prevent them from seeing their Marine guard son, the mother and stepfather of a hostage in the U.S. Embassy in Tehran took a plane for Iran today without waiting for U.S. government authorization to go.

Carter placed a ban on travel to Iran by U.S. citizens yesterday shortly after Iranian Foreign Minister Sadegh Ghotbzadeh told a press conference in Tehran that the parents, Barbara and Kenneth Timm, from the Milwaukee area, could pick up visas to come see their son, Sgt. Kevin Hermening, 20.

In a strong, clear voice, Barbara Timm read out a statement at a press conference at her Paris hotel this afternoon, saying:

"With all due respect, Mr. President, I would like to respond to your statement that a visit to our hostage would be too emotionally trying on us. If this is the land of the free, then I want the freedom to decide for myself what I can handle emotionally." [In Washington, the White House said, "We are interested in and concerned about" the Timms' arrangements. A senior official said that it was illegal for them to go to Tehran but that this matter would be decided by the Justice Department. He expressed concern that "this family would be very cynically used and manipulated by the Iranians."]

Mrs. Timm, who was divorced from Sgt. Hermening's father, said that there has been a Red Cross doctor's report showing that her son is "suffering emotional damage, as are all the other hostages." While he is "a brave, strong young man, a model Marine," she said, "I must do what I can to help him want to face each new day as a hostage, to help him keep his faith."

"If," she said, "he must die as a result of military action, then he must not die with the feeling of abandonment of family or country . . . He will die with the knowledge that we, his family, did everything in our physical power to help save him. He will die in peace and I can live in peace with myself."

Addressing Carter directly, she said "Do not deny my right to reach my son. Do not deny my right to understand another culture, another people . . . With the grace of God, keep our two lands from war."

The Timm's lawyer, Carl McAfee of Norton, Va., told reporters after the press conference that an official in the U.S. Attorney General's office had said that the president thought it would be too much of an emotional strain for the family to visit their son, the youngest of 50 Americans held hostage since Moslem militants seized the U.S. Embassy last Nov. 4.

The lawyer said he thought the timing of Carter's statement was designed to prevent the Timms from going to Tehran. He said that they had not planned to leave Paris until Saturday evening at the earliest.

A source close to the family said that the change in plans came after McAfee spoke by transatlantic telephone with his law partners and with Rep. George Hansen (R-Idaho) in Washington. The sources said they told him the family would not be granted special permission to go to Tehran and that they had better get there fast if they wanted to avert the risk of U.S. efforts to stop them.

The source, who stayed here, said this was taken to mean that the U.S. Embassy in Paris might serve formal notice on them not to go and might attempt to seize their passports or prevent them in some other way boarding a Tehran-bound flight.

[While a senior White House official said he knew of no "commitments or assurances" that the Timms would see their son, Iranian President Abol Hassan Bani-Sadr said today that relatives of the hostages would be permitted to visit them. The militants at the U.S. Embassy had earlier rejected this idea, saying they would admit only visitors whom they had invited.]

The witness to the hotel room conversations, described as highly emotional, said that the attorney and his clients decided that if they left immediately, "it would be a mother trying to see her son, but that anything else later would look political."

John Guntner, a private detective working with McAfee who accompanied the party to Paris, said, "I can guarantee you that Barbara isn't going to vote for Carter." McAfee himself has run for office as a Republican from Northern Virginia. He also represented family interests when the crew of the U.S. vessel Pueblo was interned by North Korea. The North Koreans blocked his attempts to visit clients there in 1968.

Hansen, who has been working closely with the Timms, has been to Tehran twice and has been criticized for trying to negotiate privately with the Iranian authorities.

[The Timms and McAfee took a Lufthansa flight from Paris to Frankfurt and changed planes for another Lufthansas flight that arrived in Tehran early Saturday morning.]

McAfee had told a Paris press conference earlier that his clients were opposed to any U.S. military intervention in Iran because it would mean the death of their son. The lawyer described Mrs. Timm as "searching for what was so terrible under the shah to provoke such an action. We're looking for answers."

Asked how that search would help Mrs. Timm get her son back, McAfee replied, "It may not." She left the press conference immediately after reading her handwritten prepared statement.

Asked if the interests of the U.S. government and the hostages were necessarily the same, McAfee simply said no and added that the interests of all the hostages may not be the same. He said he saw no objection to the "piecemeal" release of the hostages, apparently implying that he thought it might be possible for him to arrange the individual release of Sgt. Hermening.

McAfee said that Hansen had filed a formal request for authorization for the Timms to go to Tehran shortly after Carter had announced that family members could go only with the permission of the State Department or the attorney general.

Meanwhile, Iranian Foreign Minister Ghotbzadeh showed up in Paris today on an unannounced "private" visit. French sources close to him insisted that his trip here in a private plane was unrelated either to the hostages or to U.S. sanctions against Iran.

They said that Ghotbzadeh, who had lived here for years as a political exile, was only here to pick up personal documents.

Shahpour Bakhtiar, the last Iranian premier before the Islamic revolution, gave a press conference here today in which he said that he had visited Iraq to consult there with other Iranian opponents of the revolutionary government. "I didn't knock on the door, I was invited," he said.

"He opposes the use of neighboring Iraq as a base for a military reconquest of Iran, he said, but he added that he had no objection to commando operations by the United States or others that would damage the Iranian oil-producing facilities centered near the southern border with Iraq.