WASHINGTON - President Barack Obama will say on Tuesday he is sending 30,000 more U.S. troops to Afghanistan by next summer to speed the battle against the Taliban and plans to bring some soldiers home in 19 months.

The accelerated timetable Obama will unveil in a high-stakes speech surprised some Pentagon planners who expected a 12- to 18-month period for deploying forces to bolster the 68,000 U.S. troops already in the war zone.

The 30,000 additional troops that I am announcing tonight will deploy in the first part of 2010 -- the fastest pace possible -- so that they can target the insurgency and secure key population centers, Obama will say, according to excerpts of his speech released by the White House.

Obama is due to speak at 8 p.m. EST (0100 GMT Wednesday) at the U.S. Military Academy in West Point, New York, with the challenge of convincing war-weary Americans and leaders of his own Democratic Party of the need to step up the fight in the eight-year-old war launched after the September 11 attacks.

The anticipated $25 billion to $30 billion needed to fund the 30,000-troop surge will push the overall cost of military operations in Afghanistan to nearly $95 billion for this fiscal year, eclipsing the $61 billion to be spent in the same period on the Iraq war.

Major U.S. troop movements are not expected before January and all 30,000 troops should be in place by the end of August, defense officials said. Obama will say he expects allies to announce troop increases of their own.

Our friends have fought and bled and died alongside us in Afghanistan. Now, we must come together to end this war successfully, Obama will say.

For what's at stake is not simply a test of NATO's credibility. What's at stake is the security of our allies and the common security of the world.

Senior Obama administration officials said the president's decision to start bringing the troops home by July 2011 represents a faster exit timetable than any of the options presented to him during a three-month review of Afghan policy.

Just as we have done in Iraq, we will execute this transition responsibly, taking into account conditions on the ground, Obama will say.

A Republican congressional leadership aide said Obama made clear in an afternoon briefing with lawmakers that the July 2011 withdrawal timetable will be dictated by the conditions on the ground.

(Additional reporting by Adam Entous, Phil Stewart, Ross Colvin, Susan Cornwell, Jeff Mason and Matt Spetalnick; Writing by Steve Holland; Editing by John O'Callaghan)