Tony Sickmann, the mother of a young Marine hostage, is not planning to go to Tehran.

"I would not do that to our Rocky," Sickmann said of her son, Rodney, a 22-year-old Marine sergeant from Krakow, Mo. "If we went over there, it would pull him completely down."

For the hostages' families, Barbara Timm's journey to visit her son, Marine Sgt. Kevin J. Hermening, 20, has been a bittersweet drama, mixing deep yearnings with fears of painful departure.

"If she got to see her son and can walk away from it, that's good," said Pat Lee of Falls Church, whose husband, Gary, a 37-year-old general services officer, is a hostage. "I would find it very difficult to see my husband and walk away from it."

Nevertheless, some captives' families drew encouragement from Timm's trip and say they hope to visit Tehran soon, despite President Carter's ban on travel there and U.S. efforts to discourage journeys by hostages' relatives.

"I would love to go if it can be arranged," said Dorothy Hall, of Little Falls, Minn., whose son, Joseph, an Army warrant officer, is among the 50 Americans being held at the U.S. Embassy in Tehran. "It's a wonderful thing that she got to see her son."

The prospect of other trips by hostages' relatives was tangled yesterday in continuing behind-the-scenes negotiations and changing diplomatic signals.

White House and State Department spokesmen said Timm and her husband, Kenneth, had not technically violated the newly announced ban on travel to Iran, but that the United States would discourage similar visits. The officials left open the possibility of authorizing exemptions from the ban, which they said goes into effect later this week.

Among those trying to clear other trips were Rep. George V. Hansen (R-Idaho), who visited Tehran earlier in the crisis; representatives of a law firm that helped arrange the Timms' trip, and the Committee for American-Iranian Crisis Resolution, which has sent several delegations to Tehran recently, including the clergymen who held Eastern services at the embassy.

Norman Forer, a social welfare professor who heads the Kansas-based committee, said his group has the approval of Iranian militants for three more families to travel to Tehran. He declined to identify them, saying any announcement should come from them.

Dorothy Hall said yesterday that she expects to go on the trip arranged by the Kansas-based group if U.S. government clearance is obtained. The Graves family of Reston also plans to go. There were conflicting reports about the identity of the third family.

The trip "could very well be late this week," said Luzette Graves, daughter of a hostage, public affairs officer John E. Graves, 52. The chief aims of the trip, she said, would be "to see our loved ones" and to let the hostages know "that they haven't been abandoned, at least by their families."

The Graveses have been among the most outspoken of the families, recently calling for a congressional investigation of past U.S. actions in Iran. In a telephone interview over the weekend, Alan Graves, John Graves' son, said that doubts about Carter's policies in Iran were a factor in his family's desire to visit Tehran.

"I really don't buy what the media's been saying. I really don't buy what Carter's been saying," Alan Graves said. "It only leaves one alternative -- to go over and see for ourselves."

Other hostages' relatives have expressed fears, however, that visits to the captives may result in propaganda and delay the captives' release. "I can't believe that there will be any positive results here," said Margaret Lauterbach of Dayton, Ohio, whose son, administrative employe Steven Lauterbach, 28, is a hostage.