SIOUX FALLS, S.D. (AP) _ The Kerrey campaign's charter plane is such an old relic, aides thought it worthy of a name-the-plane contest. The candidate himself came up with The Flying Pig.

''Haven't you ever heard, when pigs fly, Bob Kerrey will be president?'' the Nebraska senator joked aboard the noisy 50-seat Convair turbo-prop that carries staff, Secret Service agents and reporters as the campaign hops around the country.

''Moby Dick'' was another entrant, because the plane is ''big and blue and moves kind of slow,'' one Kerrey aide explained.

About 30 years old, the Kerrey plane is smaller than the sleek jets being used by some of the other campaigns. But Kerrey should feel comfortable in it; the Convair is the same model used in jump school when he was training to be a Navy SEAL.

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Kerrey was sitting on a tiny school chair, discussing the issues with the director of the Tremont Day Care center while 2- and 3-year olds ate cornflakes out of tiny bowls around him.

''Watch out for the airplane, it will hurt you 3/8'' one talkative youngster kept repeating, as a TV boom mike came down through the air near where he and the candidate sat.

The boy twisted and talked non-stop amid the crush of reporters, lights and cameras, drawing smiles from Kerrey and everyone else in the room.

''Your last name isn't Agran, is it?'' Kerrey teased, tousling the young boy's hair.

The day care center was Kerrey's first campaign stop after Sunday night's debate, in which longshot Larry Agran made a colorful debut, sniping at rival Jerry Brown and drawing laughs by holding up a sign of his own 800-number.

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Brown marveled at small army of Secret Service agents crawling through the Howard Johnson's in Sioux Falls for the South Dakota debate, and wondered aloud why Kerrey and Bill Clinton need their protection.

''What's the game? The illusion of power, is that it?'' Brown said.

To qualify for Secret Service protection, a candidate must first meet a certain fund-raising threshold. Clinton and Kerrey both decided to take advantage of the extra protection.

Secret Service protection means that a band of stern-looking agents wearing earphones constantly flank the candidate, and local police show up to provide a motorcade.

In Denver, the Kerrey campaign asked not to have the roads blocked, but a motorcycle officer whipped around and forced traffic to pull over anyway.

''This guy loves it - we can't get him to stop,'' a Kerrey aide said.

At a ranch near Rapid City on Monday, Kerrey took time out for a quick horseback ride. A Secret Service agent known for his riding ability was ready in jeans, so he could plod along right beside the candidate. A truck full of the suited agents trailed along.

Kerrey was asked if he had the agents in tow to look more presidential. No, he said, and ''as a matter of fact, if anything, one of the problems you get, Secret Service can make it difficult to get to people.''