The economy grew at a rate of 1.9 percent from January to March.
The April-to-June figures for the gross domestic product aren't yet in, but some economists have forecast them to be lower.
Geithner says growth for the first half of 2011 will probably come in at 2 percent, perhaps even slightly lower.
Geithner blames slow growth on rising oil prices, bad weather, the nuclear crisis in Japan, and tight budgets for local and state governments.
He also says the specter of a government default is taking a toll.
Geithner spoke on "Fox News Sunday" and CNN's "State of the Union."
(Copyright 2011 by The Associated Press. All Rights Reserved.)