Tom Donilon is one of those Wunderkinder who spring out of nowhere to become driving forces in politics. And he was the one President Carter called to congratulate in the afterglow of last night's rules victory. "[Donilon] is the hero," said Carter adviser Hamilton Jordan.

It is the eve of the Democratic convention and everyone wants "The Kid" -- Carter/Mondale team's 24-year-old don of the delegates, in charge of finding, keeping, counting and holding those 1,985 crucial conventioneers.

Tom Donilon leaves the sanctity of his Sheraton Center sixth-floor hideway and is mobbed by a piranha-school of reporters: "No," he says, pressed for information on how the delegate count is going on the rules fight. "I'm not giving head counts. You guys just want to find the defectors."

Donilon is the son of a Rhode Island Irish-American pol. He is tall, chubby- cheeked, freckled, but with the pallor of one who rarely sees daylight. cHe is never far from a phone, the lifeline of his existence. The beeper on the belt of his baggy navy pants wires him to the top -- Carter campaign chieftains Hamilton Jordan and Bob Strauss, and presidential press secretary Jody Powell. All want him.

Donion races off with Jordan and Vice President Mondale's top aide, Richard Moe, to lay ground rules, explore compromises with the Kennedy forces for tonight's platform fight.

Then on to Strauss and Jordan:

"I have to brief those guys," he says. On the phone to a Kennedy aide: "I'm telling you right now you can't have 40 minutes [for tonight's demonstration when Kennedy addresses the convention]. Ten minutes of clap, I've got no problems with. But your people are talking balloons, confetti, bit. We got the Hubert Humphry film, the Reagan attack s---. If you guys want 40 minutes, it's got to come out of the economic debate . . . "

Hard deals from a young pol at his very first convention.

Sunday night. High atop Manhattan. The Rainbow Room, Strauss and Powell and Jordan glitter in the mob at the Newsweek party. Meanwhile, Donilon is still tracking; hunched over a phone in a cigarette-stale hotel room, giving marching orders.

Carter's top aides sip their drinks and speak almost revently about Donilon. His vital job of holding onto the delegates began in March 1979. Now he is translating his computer-like knowledge into overseeing the massive Carter army that floods the convention floor.

Donilon is described as that rare combination of tactician and conceptualizer; a boy-genius on details, yet unencumbered with terminal cockiness. There is that almost appalingly youthful zest -- the ability to crash through a brick wall, no questions asked, for the cause -- coupled with a total lack of awe for his elders. "For a 61-year-old man," he says casually of Strauss, "he has an amazing ability to work long, hard hours."

Some of the press, expectedly, do not share the enthusiasm of the Carter/Mondale crew finding Donilon "filled with self-importance." When one newspaper heavy went testily at Donilon, badgering him about platform details, Donilon quietly told him to look up the facts himself. "He wanted me to teach him the Democratic platform. He was embarrassing himself in front of his colleagues," Donilon says. "I just told him to go look it up."

Through his expertise, Donilon has become so crucial that some in the Carter camp refer to him as Hamilton Jordan's alter ego.

Says Jody Powell: "He really helps make key decisions. I wanted to go all out on that rules proposal, but Donilon convinced us not to." (Powell was referring to the presidents concession requiring potential nominees to give delegates a written statement of their views on the platform -- including a pledge to carry out all its recommendations they do not specifically repudiate.) "I think we could have won it, but Donilon convinced me it would be close and we might not look so good on it."

The attitude in the Carter camp for several days was that they had the so-called "open" convention vs. "faithful delegate" rule fight locked up. "Donilon always had a sense of where we were in the rules question," says Dick Moe.

When the Billy Carter-Lybyan flap roared through the national press, Donilon met Bob Strauss, who hastily returned from a vacation to help with the brush fire. The Harris poll was grim. grim.

Donilon turned to Strauss in the car and said, "If we're going to lose this thing [the open convention challenge] we'll lose it in big blocs in urban areas -- New York, Philly . . . This is your milieu. You're the only one who can talk to these guys."

Donilon set it up -- county leaders, local pols all got the Strauss treatment. "We did it in every state," says Donilon.

"Ten days ago there was a lot of apprehension," says Moe. "Donilon reflected that -- and if he gets nervous, everyone gets nervous. Last week, when Donilon started to feel better everyone started to feel better. You could feel that confidence ripple out," Wonder Kid

Tim Smith, Carter/Mondale chief counsel, is in Donilon's room Saturday afternoon. "I'll tell you how we found Donilon. It was one of my greatest contributions." Smith was one of the first to go from the White House to Carter/Mondale in early '79. "I needed a million things done on delegate selection. I was given an exact profile -- you should find a young genius who will be this year's Rick Hutcheson [the 1976 delegate hunter]. I interviewed a lot who were decidely non-geniuses. And then Frank Moore says, "I got this guy. This kid. He's an intern in my office' (of White House liaison to Congress). And then he did an imitation of a computer. Moore said, "If you say to this kid -- the 23rd district of Ohio -- he can tell you demographics and vote totals for the last three elections. It's in his blood. He combines a brilliant academic record in political science and knows how to talk to ward healers. He can talk to govenors, labor union presidents, anybody."

The subject of all this praise is pretty close to blushing by now. There are howls from three Carter aides clustered in the room as Smith makes a parting crack, "He's cocky -- but cute."

Donilon gets back to business, shouts from one room to his assistant, Melissa Reese, "Get Dick Moe on the phone," then an intense," Get [campaign manager Tim] Kraft up here . . . I got Cosentino on the line." Kraft comes quickly to the sixth floor, as Donilon mutters a "goddamn it."

Illinois State Treasurer Jerry Cosentino, Carter man and delegate co-chairman, had been wooed by Kennedy forces for days as a possible defector. cNow Cosentino is telling Donilon that he is meeting with Kennedy the next day. But things calm down after the phone call. Cosentino is staying in line.

Then Donilon talks to a Kennedy aide -- in the jocular cadence that comes from being friendly enemies. "Is Kennedy seeing Cosentino?" he asks, as if he didn't know. Then the laugh and a chiding. "Why don't you stay away from our people?" They talk about going on a fishing trip when this is all over. "Just make sure you bring a Rolling Stones tape."

Donilon hangs up the phone. "That's the thing people don't understand. This is not 1972. There are some animosities, but many of us are really friends. We talk back and forth all the time. Their candidate is the problem. And you got a camp of crazies over there in guys like [assistant] Jim Flug and [speechwriter] Bob Shrum.

"I think Kennedy was hurt himself badly. After Illinois we had the nomination won. This rules fight hasn't helped him. He looks like a political opportunist. But like most human beings, its hard for him to say no. It's like studying for a final exam. You know you have to do it -- but you put it off. With Kennedy it's been kind of static. He's avoided making a decision. I don't think he's thought about what he will be doing next week. aHe's playing it by ear, as he has the whole campaign." Politics for Supper

Listening to the faint New England accent, looking at that Irish face, often leads to the knee-jerk assumption that Donilon should be a Kennedy man. o

"John F. Kennedy was a hero where I came from -- Irish-Italian inner-city Catholic ghetto." His neighborhood in Providence, R.I., was second and third-generation Irish and Italian. The reverence was for John and Robert -- "but I never saw any great reverence for Ted."

Donilon says his was "your average Irish Catholic household." His mother is a clerk in an elementary school. His father "works for a business that buys steel." He is also a local politician, active on the school board.

Where he comes from, says Donilon, "everyone is political. I can't remember a dinner-table discussion when we didn't discuss two things -- either schoolwork or politics." Donilon got straight A's at LaSalle Academy, then at Catholic University. (He vaguely remembers getting a B in freshman Latin.)

His family spawned achievers. His sister is a nurse, one brother at Georgetown University is being nominated for a Rhodes scholarship, another is studying acting. "My dad shakes his head about that. A son who wants to be an actor." Is there any of the Irish ham, the Irish singer inn Donilon? He laughs. "Only when I drink."

This past year he has worked seven days a week. "All he does is work," sighs Melissa Reese. One day months ago she rode her bike to work. It's been chained to a desk ever since; she hasn't left work early enough to ride it home.

Donilon says modestly that he is "just filling a vacuum." There are a lot of jokes about his age: He was one of those party reformers in 1972 -- in the seventh grade. He says now at the ancient age of 24, "I've learned more in this than in any experience of my life. It's a high-cost, high-benefit job.

"I learned about my ability and limits -- that I can get a lot done in a day and have a pretty good ability to come up with a concept and carry it out.

"Probably the most salient thing I learned is that the press isn't a neutral observer but a full-fledged fact of the political force. There's always a 'little press hit on this' and how to portray something in the media. I'm disappointed in the press to a large degree, in that they value the story -- rather than the substance of an argument. And they are easily misled by catch words -- like 'open' convention."

Donilon uses political jargon but is new enough to have the grace to blush at such phrases as "we were behind the PR curve on that one." He laughs. "Politics really abuses the English language. I used to be able to speak it."

He voted for Carter four years ago, the first time he could vote, and will work hard through November to elect him. But win or lose, Donilon is going to law school. His dream always has been to be a lawyer. His Carter mentors who are a quarter-century older look almost wistfully at him and say, "He's got a great future in politics."

That future does not, says Donilon, include elective office. "There are a lot of unfair demands, a lot of nonsubstantive aspects I don't like, a lot of things that are kind of dumb and demeaning."

Donilon lives in a sort of political Animal House near Catholic University with six buddies he has recruited into the Carter camp -- all bright political-science graduates.

He used to be a great reader of history, but that has gone by the boards during this campaign.His love for politics has cost him in other areas. "I lost a girlfriend -- brilliant, beautiful med student at Georgetown. She didn't like politicians, couldn't consider any of them different, thought they all were selfish." There is little private time for sports or fun. "As I say -- I used to have a girlfriend I played racketball with." Cracking the Whips

It is just hours before the convention opens Monday afternoon and nothing is left to chance. There are whips all over the place -- forming an elaborate, grand pyramid. The phrases sound like some X-rated movie run amok -- "cluster whips" and "state whips" and "line whips." Hundreds upon hundreds of the cadre.

Donilon is the central link to the whole floor operation. He and other aides like convention director John Rendon have worked it out to the finest detail. There are 14 cluster whips and each cluster leader (two to a cluster) has a person to answer directly to in the situation trailer. At 4:30 the scene in the trailer is already bedlam: four televisions at full-blast, six volunteers grabbing phone calls, operatives barking orders, and in one corner Rendon and Donilon staring out at the milling chaos.

Jordan and Donilon and other leaders will be there. Four other trailers are nearby: the boiler room, VIP trailer, press, scheduling. When a decision is made on how the delegates should go on a vote, it is relayed from Donilon out to the 114 desk leaders and in turn to the 14 cluster leaders and on down through the chain of command on the floor.

Donilon has it worked out so that each Carter tactician has about seven delegates for whom he or she is responsible. "We figure we can reach everybody in seven minutes," he says.

More importantly, after the Republican rumor mills cranked up on Gerald Ford, Donilon and company have instituted a (hopefully) fail-safe block on rumors. The operation is set up two ways -- orders go from the top down but also from the bottom up. If a rumor starts on the floor it will be relayed up to the top, it can be either confirmed or denied and the information trickled on back down to the delegates. Donilon figures they can stop any rumor within 20 minutes -- enough time, he hopes, to stop the networks from swinging wildly.

And all that computerized knowledge Donilon has picked up on the delegates has been relayed to his situation leaders. Each one has a black notebook -- and each notebook has a detailed report on every delegate -- what issues are key to them, who can be contacted to influence them.

Donilon knows all 1,985 well. He has been living with them for months. 'Donilon for President!'

On the floor Monday night, as the "open" rule was debated, cries of "Stay free!" from Kennedy delegates were drowned out by thunderous cheers from Carter delegates.

Outside the hall at the trailers, Donilon, Jordan, Strauss, Powell, Moe and Pat Caddell watched the roll call of states on TV -- joking, laughing, gulping water from the cooler. About 8:15, Pennsylvania put the Carter side over the top. One huge cheer rose from the trailers. According to Donilon's unofficial tally, the vote was 1,936 1/2 to 1,390 1/2. "Very little slippage," Donilon said with a beaming smile.

A huge box of Godiva chocolates was passed around. Donilon hugged and twirled one woman staffer as he moved from the situation trailer to the VIP trailer, where Jordan and Powell were carrying on. As Donilon entered, there was a loud cheer of "Donilon for President!"

Speaking of presidents, Powell made quite a point out of the fact that Donilon was the only one of the staff to get a call from Carter immediately after the win. Powell, in TV makeup, spread the name of Donilon, the virtual unknown, to the TV audience. He confessed he really didn't know what the president said. "I've got to go get a complete fill from Mr. Donilon. When these 24-year-olds win their first convention fight, they figure they don't have to talk to senior staff people," Powell quipped.

The president, said Donilon with a smile, "asked me if he could take Rosalynn off the phones to the delegates now."

As Powell began a mini-press conference outside the trailer, he joked, "I am the warmup man for Donilon."

"Who?" chorused some of the bewildered press who knew little of Donilon's role.

Then Donilon, the boy wonder whom Walter Cronkite and company had not clamored for, came forward, a tally sheet in his hand. "We had extreme pressure in New York and Illinois, and the results there are particularly gratifying."

Meanwhile, Hamilton Jordan, the president's chief adviser, came up quietly at the back of the mob. A reporter turned toward him and asked him a question.

Jordan looked back up to the steps of the press trailer where Donilon was patiently giving out the results.

"Y'all pay attention to Tom," Jordan admonished. "He's the hero."