The Cupertino, Calif., company declined to give a reason for the shipping delay, but said would-be customers can still pre-order the iPad for in-store pickup on April 3, or purchase the device in stores that day.
The iPads going on sale will connect to Wi-Fi networks only and cost $499, $599 or $699, depending on the data storage capacity.
Versions that also can connect to "3G" cellular networks are expected to go on sale in late April for $629, $729 or $829.
International releases also are planned for later in April.