WASHINGTON — Treasury Secretary Timothy F. Geithner warned Wednesday that the necessary rebalancing of the economy was “at risk of being undermined” by countries trying to prevent their currencies from rising in value.

Mr. Geithner, in a speech at the Brookings Institution, said that some of the world’s biggest economies should “focus on strengthening growth, rather than risking a premature shift to restraint” by cutting government spending too rapidly.

His message — aimed at countries like China and Germany, but also an appeal for support from other major economies — came as the International Monetary Fund predicted that the world economy would grow 4.2 percent next year, down from the estimate of 4.8 percent for this year, but that “a sharper global slowdown is unlikely.”