When Ronald Reagan, the nation's oldest president, is inaugurated Jan. 21 he expects to draw thousands of young people to Washington with a series of pageants and concerts, balls and forums -- all designed to woo and win the under-30 set as Republicans for life.

That generation, the 18-to-29-year-olds, handed the president nearly 60 percent of its vote on Nov. 6. Now inauguration planners, heartened by the dramatic turnout for a politician who was once booed and jeered on college campuses, want to thank the young voters and continue a campaign to lock them in to the GOP.

"They are in our court, and that's the bottom line," said Ellen Conaway, a campaign adviser to the Reagan youth operation last fall. "We want them to know there is room for them, that we welcome them, that they are our future leaders."

The young voters have already gotten the message.

"Obviously they're courting us," said Bill Healy, a junior at Notre Dame who got one of the coveted invitations to an inaugural event. "It just shows that now that the election's over, they're not going to dump us. They see they have a good chance to get us, and they're sending out their message. Ronald Reagan is a master at that."

The courtship will begin in earnest with a Youth Leadership Forum Jan. 19, when more than 3,000 young people have been invited to hear Vice President Bush speak. A White House aide is lining up members of Congress, astronauts and other "young American leaders" to address the young people, according to inaugural staffers.

During the rest of the weekend, rock stars like Kool and the Gang and rock 'n' roll greats like Jerry Lee Lewis will serenade the young people. More than 3,500 students, brought in from all over the country, will entertain other young people at a pageant. And the president himself will put in an appearance at an inaugural ball especially for young Americans that planners say is a first.

"In 1981, the feeling was the inaugural tended to be too exclusive, too upscale, too old," said one GOP strategist. "This time the feeling will be less upscale and more youthful. We're going to drive to our new strengths."

First among those strengths is the young voters, particularly those 18 to 24 years old, who, according to presidential pollster Richard Wirthlin, "broke with history" last November. According to Wirthlin, the Democratic Party failed to get a majority of those voters for the first time since 1972, when 18-year-olds got the right to vote.

"It was a phenomenon," said White House aide Michael K. Deaver, who is general chairman of the inauguration. "We'd all be crazy if we didn'tcontinue to work on that voter group. It is the future."

But it is a future that is uncertain, a generation "up for grabs by either party," according to Lee Atwater, who was deputy director of Reagan's reelection campaign. "We can't rest on our laurels. We did unusually well with the youth vote in 1984. We'll have to do a lot to sustain that."

For one thing, the Democrats are not going to give them up without a fight.

"If the generation that gets turned on to the music of Boy George falls in step with the party of Jerry Falwell, I'll be very surprised," said Democratic National Committee spokesman Terry Michael.

"I know what they're banking on . . . . The talk is, get them to vote once or twice for you, and you've got them forever. But this is a volatile generation, one that's grown up completely on television. Things can change with the flip of a channel."

It took 20 years for the Republicans to get this far. When Atwater was a youth coordinator for Richard Nixon in the '70s, the campuses were no place for the GOP. Deaver said he can remember Reagan's 1965 campaign for the California State House, "when we avoided campuses like the plague."

But now that the young have jumped on board, it is still a fragile allegiance.

"Young people have a short memory span," said Brian Berry, a 26-year-old Montgomery County advertising executive who headed Reagan's youth campaign in Maryland. "This election we compared Jimmy Carter to Ronald Reagan, and Reagan came up the winner. If in 1988, young people find that deficits are causing an economic downturn, you'll see them slipping away from the Republican Party."

Other young people said that they support the Republican Party's emphasis on fiscal restraint and a strong defense, but disagree with the New Right social agenda adopted by the party, especially its opposition to legalized abortion.

"I believe so strongly in the main philosophy of the party," said Jacki Von Ekeren, 20, who worked for Reagan on the Iowa State campus. "But I don't want to see the party get too carried away down that road of Jerry Falwell's. I don't want to see more Moral Majority."

And Berry cautioned: "We can't hope young people will join in because of Ronald Reagan because Ronald Reagan ain't going to be there in '88."

Indeed, much of the young voter's support was based on Reagan's personal appeal as a charismatic leader and his message, as Atwater sees it, of "optimism, growth and opportunity."

"My generation was politicized under two administrations: Carter-Mondale and Reagan," said Liz Pickens, the 24-year-old Texan who headed Reagan's national youth campaign. "Carter was all doom and gloom . . . . But Ronald Reagan is our Indiana Jones. You know, no problem too big to handle."

Pickens coordinated a campaign with 50 state chairmen and 650 campus coordinators that registered more than 264,000 college-age voters.

"Youth campaigns have traditionally been given a few buttons and a pat on the head, but we were given money, support and credibility . . . . The president even came to visit our office once," Pickens said.

Campaign media director Doug Watts met with Pickens' group and came up with a $75,000 project in which an eight-page tabloid was produced by college students and inserted in college newspapers at 76 campuses the week of the election.

Pickens capped off her voter registration effort with a project she dubbed "Mission Possible," after the old "Mission Impossible" television series.

Her campus coordinators were sent tape recordings telling them, "Your mission, if you choose to accept it, is . . . " getting out the Reagan vote. The tape included the voice of the president asking for their help, and a dossier marked "top secret," complete with photos of their targets: Jimmy Carter, Walter Mondale and House Speaker Thomas P. (Tip) O'Neill Jr. "At the University of Texas they had a former FBI agent, wearing a trench coat, come on campus and deliver it," said Pickens.

But this elaborate courtship of the young has not been confined to the campaign trail. At the Republican National Committee (RNC), communications director Bill Greener is seeking a better body of data on the young voters. "We need to know what their 'hot buttons' are . . . the issues they care most about, the rhetoric," he said.

Both Deaver and the RNC's director of political operations William B. Lacey said the next few years will be critical in keeping the young voters. "We don't have a lock on any voter group," cautioned Deaver.

Lacey said the "keystone" of their effort will be "the president's leadership and effectiveness. That has to continue. Our policies must demonstrate that we are putting our money where our mouths are. We must be perceived as the party of economic opportunity."

"I don't think it's any easy job . . . but it's a lot easier for us to hold them than for the Democrats to take them away."