For the second time this week, President Bush formally notified Congress on Friday that he is sending U.S. troops into combat in Iraq.

The notification was made under the 1973 War Powers Resolution. The law requires congressional approval if troops remain in a conflict for more than 60 days. Congress already gave its approval in October as part of a resolution authorizing force against Iraq.

On Tuesday, Bush notified Congress that he was invoking that October resolution.

In his letter Friday, Bush said the Iraqi military operations "have been carefully planned to accomplish our goals with the minimum loss of life among coalition military forces and to innocent civilians."

Bush said it is not known how long the war will last, how many troops will be needed or when they can return.

Congress passed the law as the Vietnam War was winding down to make sure it gave its approval to any major conflict. Presidents of both parties have questioned its constitutionality. Bush's letter said the notification was being made consistent with the law.