The decisive influence in the development of President Carter's competitive instincts was the game of Monopoly to which he was addicted in his childhood, according to his sister, Ruth Carter Stapleton, who has been a busy woman lately.

This is easy to understand. Anyone who has won second prize in a beauty contest is bound to spend the rest of his life chasing after those who can vote.

"I wonder if the White House was won in a dining room in Plains," Stapleton writes in the current issue of Ladies' Home Journal. "That will to win certainly was honed, if not forged there." While games of Scrabble and Parcheesi also were popular, the Carter children's favorite activity was Monopoly, she says.

She said, "No one hated to lose more than Jimmy." Well, we already knew that. The important question, to the student of political history, is not whether he won or lost, but how he played the game.

To begin with, which marker did he choose? The automobile (speed and urbanism)? The horse (tradition and land-orientation)? The iron (diplomacy)?

Did he vie to be banker himself, or did he try to find a reliable friend to do it for him?

What kind of property was he interested in acquiring? Did he skip the low-rent districts (Baltic, Mediterranean) and only go after the classy yellow, green and blue neighborhoods? Or did he devote himself to taking run-down areas and revitalizing them with subsidized housing and hotels that might give them a new prosperity?

How did he feel about railroads?

When he landed in jail without passing Go, did he serve his term or slip $50 to the bank and run for it?

How did he manage his budget? Did he mortgage himself to the hilt? If he had to choose between paying $200 in taxes or 10 per cent of his worth, did he know which to choose? What kind of a landlord was he? How did he treat a poor tenant who couldn't afford the rent?

In any case, what kind of an economic picture did Monopoly leave in our President's mind? In talking about the cost of living earlier this year, he mentioned that his wife might occasionally buy a dress for $25. He probably also thinks, as a result of Monopoly, that you can build a hotel on Connecticut Avenue for $600, a row of townhouses on Pennsylvania Avenue for $200 each, and spend the night in a hotel right on the Boardwalk for $50 for a single.

And most significant of all - when he was the biggest property owner and landlord in town, with houses and hotels all over the place, how did he behave when he was told he was being assessed $40 a house and $115 a hotel for street repairs?