WASHINGTON — Citing “huge challenges” ahead, President Barack Obama says he still intends to withdraw 33,000 troops from Afghanistan by next year and says the administration’s strategy for winding down the war remains unchanged.

Pres. Obama made his declaration in a letter to congressional leaders Friday. The letter accompanied a semiannual report assessing the administration’s policy toward Afghanistan and Pakistan.

The letter reports improvement in the fight against al-Qaida, as well as a reversal in the Taliban’s momentum in Afghanistan and headway in the training of Afghan security forces.

“Huge challenges remain, and this is the beginning — but not the end — of our effort to wind down this war,” Pres. Obama wrote.

The 33,000 troops represent the force surge Pres. Obama announced in December 2009. Last June, he announced the withdrawal of 10,000 U. S. troops from Afghanistan by the end of this year and that the 33,000 surge troops would leave Afghanistan by the summer of 2012.

In his letter, Pres. Obama said that plan was still on track.