For the families of at least five American hostages held in Lebanon, the gulf of separation closed a bit yesterday as their captured relatives, led by a forceful young oil-field salesman from Houston, appeared on their television screens.

The families of other hostages were buoyed by the calm, confident performance of hostage Allyn Blair Conwell, 39, at a Beirut airport news conference. Conwell, the captives' elected spokesmen, said he had seen most of them and could "verify beyond any doubt that they are primarily and A-No. 1 in good health."

"He's very cool and calm and collected and, as we can see from these pictures, under pressure he maintains it," Lois Conwell told CBS News at her Houston home.

Later in the day, five hostages who had not appeared before reporters sent tape-recorded messages to their families through an ABC News crew.

Conwell, an oil-field equipment salesman in Oman for Enterra Oil Field Services Ltd., grew up in Houston and Moreland, Ind., a small town 60 miles southeast of Indianapolis, where his father, Byron, lived after the parents were divorced.

"He was a leader," said Conwell's stepmother, Rosetta Conwell, in Moreland. He played varsity basketball and was senior class president at Moreland High School.

Conwell was returning to Oman from a vacation with his wife's parents in Corfu, Greece, when TWA Flight 847 was hijacked last Friday. His wife, Olga, a Greek national, and their two children had planned to return with him but decided to stay longer with her parents.

Terrie Paige Smith, 19, his daughter by his first marriage, had planned to join him as part of a high school graduation gift of a trip around the world, Rosetta Conwell said, but her passport did not come through in time.

Showing some of the same self-command as her suddenly famous son, Lois Conwell said after she saw him, "My first thought was that he looked much better than I expected. I was looking for someone bedraggled. His clothes looked nice and he looked like he'd been well-fed. His voice sounded a little tired, but I noticed it picked up more composure as he spoke."

Conwell's sister-in-law, Diana, was "crying . . . just drained" after seeing the television broadcast from Beirut airport, according to the Rev. Scott Smith, pastor of the Houston church attended by Conwell's brother, Mike, and his wife.

Javier Santos, brother-in-law of hostage Vicente Garza, 53, of Laredo, Tex., said the family was "elated" to see and hear Garza at the news conference. Garza told reporters that he and his son-in-law, hostage Robert Trautmann Jr., 37, are safe and asked his family to pray for him.

"We're just extremely happy that they're both together and safe," Santos said. "We are glued to our TV set. This was like a tonic."

Jorge Garza, Vicente's brother, said, "It gave the family a lot of hope. Now I know he's going to make it." Vicente will turn 54 in August, his brother added. "We're all going to have one heck of a birthday party."

Hostage Arthur Toga, an assistant professor at Washington University in St. Louis, also spoke at the news conference. "I miss my wife very much," he said, verging on tears. "I want to go home . . . very badly."

Toga holds a PhD in neurosciences and directs the Neuro-Imaging Laboratory of the university's School of Medicine. Describing Toga as "a bright young neuroscientist," a department head, Dr. William Landau, said, "We are pleased that he is alive and well."

Kelly Cullins of Burlington, Vt., watched as her husband, Thomas, spoke at the news conference, "It was wonderful to see him looking as good as he did," she said, "but he is still in a horrible and frightening situation."

She said he looked "tired, thin, but very alert," noting that he was "constantly glancing around" and "keeping aware."

Conwell told reporters that he had seen all the hostages except the three TWA crew members, who were interviewed from their airplane Wednesday by ABC News .

A French news service reported yesterday that Shiite leader Nabih Berri was about to release Jim Palmer, 48, of Little Rock, a hostage with a heart condition. However, Palmer's son John, 21, said last night that the State Department called to tell him that report is unconfirmed.

His father, "a big man, a bit overweight . . . who likes to square dance," had a heart attack six years ago and has been on medication since, he said. The family sent more medicine through the State Department to Palmer in Beirut yesterday, he added.

In Boston, the families of two hostages said they had abandoned an effort to unite some of the families and demand a meeting with Reagan.

"We're encouraged by the news we've had today, seeing the people at the press conference, seeing they're healthy," said Susan Traugott, sister-in-law of hostage Ralf Traugott of Lunenberg. "We are just going to step aside and watch it work . . . . Our greatest fear was that no one was doing anything."

Olga Conwell said Greek officials informed her Wednesday that they are interceding to secure her husband's release because she is a native of Greece. John Paparsenos, press attache for the Greek Embassy in Washington, would say only that the Greek government is working for the release of all the hostages. Their plane was hijacked after it left Athens airport for Rome.