The Illinois Republican had announced in August he would not seek re-election in 2008, but said he planned to finish his current term, which ends in January 2009. Republican aides, speaking on background only because Hastert had not yet publicly announced his new plans, said he now intends to leave office late this year or early next year.
Hastert's resignation would trigger a special election, probably in early 2008, in his Chicago-area district that includes Aurora and Elgin. Republicans hope to hold the seat ahead of the November 2008 election, which some fear will draw large numbers of Democratic voters unhappy with President Bush and the Iraq war.
Hastert, 65, was the longest-serving Republican speaker in history. He took the post in January 1999 after two better-known party members were forced aside by scandals and intraparty rivalries.
When Republicans lost control of the House in the 2006 elections, Hastert lost the speakership, and his retirement plans did not surprise colleagues.
Hastert's office did not respond to press calls early Thursday.