"I am an old, incorrigible atheist and I don't pray," said Stojmil V. Petkov, a Washington anesthesiologist. "But this time I have been praying."

Yesterday Petkov's prayers were answered. His wife, Trans World Airlines flight attendant Helen M. Sheahan, was released in Algiers with about 50 other hostages. She was on her way home via London and might arrive today.

TWA telephoned Petkov, a native of Yugoslavia, shortly after noon yesterday to announce his wife's release. The call came after nearly 30 hours of uncertainty and sleeplessness as he awaited word about her and about Flight 847's hops back and forth across the Mediterranean.

Petkov, 51, described the phone call from the airline. "It was fantastic," he said softly. "In the back of our minds we say it would be nice if there was someone who looks out for us in adverse situations."

About 1:20 p.m., a British diplomat in Algiers telephoned to confirm that his wife was off the 727 jet and unhurt.

After thanking the envoy, Petkov said: "Hopefully, [the other hostages] will be released, too. I hope that everything is going to end up well."

Elsewhere around the country, friends and relatives of passengers and crew aboard TWA Flight 847 kept similar vigils beside their telephones and television sets.

Like Petkov, many received good news, as the hijackers released additional passengers during the day. But for some, not certain of the fate of their loved ones, the agonizing wait went on.

Judith Chudigian of Lexington, Mass., was released yesterday morning in Algieria, according to her husband, Charles Chudigian.

"I was elated and extremely happy to hear her voice. Thank God it was her," he said.

Chudigian said he spent most of the night calling the State Department, the office of Sen. Edward M. Kennedy (D-Mass.) and TWA for information.

Like many of the passengers, including a group of about two dozen Roman Catholics on their way home from a pilgrimage to the Holy Land, Judith Chudigian was on vacation. Her husband said she was not hurt by the terrorists.

"The pilot ought to get a presidential citation," he declared.

Judith Chudigian was traveling with a friend, Paula Sukeforth, a registered nurse and mother of six. "We just saw her on television," said her husband, Harold, who said he'd been notified of her release by the State Department. "She looked very, very, very upset, concerned, withdrawn."

Other families were still waiting to hear about friends and relatives.

Michael and Judy Brown of North Miami Beach were married in New Jersey last Sunday and had left for a European honeymoon.

"I'm praying," said Leah Abramson, Michael Brown's aunt, according to press reports. "We're Jewish but Michael doesn't look Jewish, thank God. I just hope they don't hurt him. That's what worried me. Thank God, in this country we don't have to put religion on our passports."

"I am going through hell," said Dorothy Suggs of Elkhart, Ind. Her son Clinton, 29, was on the plane.

In Illinois, parishioners of St. Margaret Mary Roman Catholic Church in Algonquin held vigils for the Rev. P. William McDonnell, the pastor, who is known as Father Bill and described as "very spiritual," and 17 members of the parish who were aboard the hijacked plane.

Another Roman Catholic pastor, the Rev. Thomas J. Dempsey of St. Patrick's Church in St. Charles, Ill., was also on the Holy Land tour. "He only decided to go at the last minute," said Marian Kavanaugh, the St. Patrick's secretary. "The tour wasn't offered to the whole parish. There wasn't enough room."

Lois Conwell of Houston said she was "almost a basket case" while waiting for news of her son Allyn, 39, working in Oman for an oil-field supply firm. She said she expected that he would stay calm: "I mean I don't think he would try to jump the hijackers and take their guns."

The pilot of the plane was John L. Testrake, 57, of Richmond, Mo., who joined TWA on Oct. 12, 1953. He has lived on a 60-acre farm near Richmond more than 25 years and was described by a friend as "about the most easygoing, friendly guy you could ever meet."

There was speculation about how well Testrake would hold up under the physical and mental stress.

"He sounded so very tired, but I could tell he was hanging in there," said Jill Noble, who heard him on TV. Noble, who takes Bible lessons with Testrake and his wife, Phyllis, at the Richmond Christian Chapel, said, "So many people would have given up. I'm sure his faith in God is what's keeping him going."

Aviation officials said the Federal Aviation Administration requires two physical exams a year for pilots. The airlines usually require one as well. Bill Howell, a DC8 pilot at United Airlines, said the physicals he has taken usually include standard heart, eye, lung and other examinations, an electrocardiogram at rest, followed by exercise and another EKG and related tests.

Howell said his airline also gives a short training course on "how to handle deranged people and hijackers." It boils down to humoring them, trying to settle them down, avoiding a confrontational stance that could provoke them further, he said. It doesn't teach techniques to disarm them. TWA officials said their pilots go through crisis training but declined to describe it.

The other two top officers of the hijacked plane were First Officer Philip Maresca, 42, with the airline since 1967, and Flight Engineer Benjamin Zimmerman, 45, a TWA employe since 1968.