Mark Begich has lived with the mystery of his father's disappearance for 20 years. But it wasn't until last summer that he realized the tragedy's lingering hold on other Alaskans.

Begich was in a grocery store shortly after headlines told of new information that might lead to the plane that disappeared with Rep. Nick Begich and three others.

While he was shopping, a 40-ish man with a child walked over and introduced himself.

"This guy came up to me and said, 'I hope they find the plane,' " Begich, an Anchorage assemblyman, recalled.

They didn't. Twenty years ago today, the twin-engine Cessna 310 carrying Begich, aide Russell Brown, Rep. Hale Boggs of Louisiana and pilot Don Jonz vanished on a trip from Anchorage to Juneau. The most extensive air search in the state's history failed to turn up a clue.

In the years since, questions about the Cessna's fate have not gone away. Almost annually, the Begich family hears from psychics, historians or amateur sleuths who think they know something.

"Some of us want to know the answer, but on the other hand you want to move on," said Mark Begich. "Resolution is something you want. . . . There's a lot of folks that would like to know, too."

Nick Begich was a vibrant, outspoken Democrat a 40-year-old father of six running for his second two-year term. He had asked Boggs to come to Alaska to campaign for him, even though the Republicans had mounted only token opposition.

The opposition was Don Young, a state senator from Fort Yukon. Young's campaign was poorly financed, partly because Begich was regarded as a sure thing.

And he was. Three weeks after his plane disappeared, the congressman who was presumed dead defeated Young with 55 percent of the vote. Gov. Bill Egan had urged voters to cast their votes for the lost represen-tative, and editorial writers at the Anchorage Daily News said people should vote for Begich because he might still be alive, and even if he wasn't, a Begich victory would ensure a special election later.

The next spring, when a special election was held, Young won the seat in a race against Democratic Native leader Emil Notti.

The death of Begich changed the face of Alaska politics. Young has won every election since. With Frank Murkowski's election to the Senate in 1980, Republicans have occupied all three of Alaska's congressional seats for more than a decade.

It was Murkowski that Begich defeated to win his first term in 1970. Begich's kids are fond of pointing out that he beat two-thirds of the present congressional delegation.

They and other Democrats still like to talk about what might have been.

"If Nick Begich had not had this crash, he would be a United States senator today," said Joe Josephson, a Democrat who served in the state Senate with Begich.

"We would have always had a Democrat in Congress as part of the majority caucus, which would have been very helpful for Alaska."

In October 1972, Begich and his wife, Pegge, and Boggs and his wife, Lindy, were all scheduled to fly to Alaska from Washington for a series of campaign stops. But Congress didn't end on schedule and the campaign trip had to be compressed, so the women didn't go along.

"They had to get back for the close of Congress," recalls Lindy Boggs, who was elected to her husband's seat the following year and held it until her retirement in 1990. "Hale especially had to get back because he was majority leader.

"Hale was so tired. He didn't want to go that morning."

The group left Anchorage International Airport at 9 a.m. on Oct. 16. The trip to Juneau would have taken them through Portage Pass near Whittier and along the Gulf of Alaska to the Southeast Panhandle, a 31|2-hour trip.

The pilot last spoke to the tower at 9:12 a.m. The airplane was reported overdue in Juneau about 2 p.m.

An airport official told the Daily News that day that severe turbulence and extreme icing was reported in the pass and that an unpressurized airplane would have been unable to climb above it.

Don Jonz, 38, was owner of Pan-Alaska Airways of Fairbanks. He was an experienced Alaska bush pilot who had recently written an article in a national flying magazine scoffing at the problem of icing as a flight hazard.

"If you are sneaky, smart and careful you can fly 350 days a year and disregard 99 percent of the B.S. you hear about icing," he wrote.

More than 70 aircraft joined the search. During the next 39 days, they flew 1,000 sorties and more than 3,600 hours. By contrast, this summer's search for a plane that disappeared outside Valdez carrying five Anchorage men, including three brothers, logged fewer than 1,000 hours.

A military spy plane capable of spotting a human from 15 miles above the earth joined the search along the Alaska coastline. Lindy Boggs recalls that there were 55 sightings of something that could be wreckage, but none of it came from the plane.

The Cessna 311 had vanished without a trace. Investigators later reported that Jonz had no emergency locator beacon and no survival gear on board.

Every year about this time, Pegge Begich says she gets calls about the crash. Some come from a man in Whitehorse with a conspiracy theory. Mark Begich said a man approached him at the assembly meeting last week and offered a set of coordinates where his father's plane might be found.

Last summer, the Washington newspaper Roll Call published a story based on FBI documents obtained through the Freedom of Information Act. The records showed that the government received a report shortly after the plane disappeared in 1972 that sophisticated, experimental tracking equipment had located the wreckage of an airplane near Yakutat and that there were two survivors.

Some people brushed off the report.

"I'm sure that area was flown over and over when they were searching," Lindy Boggs said. "It was on the path."

But the Begich family felt betrayed that the information had never before been revealed to them.

"I'm firmly convinced that a serious error was made, and that's one of the reasons no one wants to come clean," said son Tom Begich. He plans to visit the site, in Icy Bay, next summer.

Meanwhile, he's carrying on the family's political legacy. A campaign consultant, he's working with Young's opponent this year, John Devens.

Pegge Begich is leaving Alaska. After two runs for her husband's old seat in the 1980s, she has gradually pulled away from the political scene. She plans to return to Minnesota, where she met Nick Begich at the age of 18.

The enduring fascination of her husband's life and death is natural, she said.

"It's a mystery. There's a fascination with mysteries. What did happen? How did it happen? . . . If the plane had been found crashed somewhere, I'm not sure this would be a story 20 years later.

"I wish there were answers. My children wish there were answers."