MARTINSBURG, W. Va. — President Bush said American troops in Iraq and Afghanistan are battling tyranny to defend the freedom that Americans celebrate on Independence Day, calling it a “vital and just” mission.

The president, speaking to a crowd of West Virginia Air National Guard soldiers and their families in Martinsburg, said he will resist political pressure to remove U.S. military personnel from Iraq.

“We long for the day when there are far fewer” troops in Iraq, Mr. Bush told about 1,000 people gathered in an aircraft hangar. “Yet withdrawing our troops prematurely, based on politics,” instead of advice from commanders on the ground, “would not be in our national interest.”

Mr. Bush’s job-approval ratings have plunged mostly because of the war in Iraq. He has fought attempts by Congress to set timetables for withdrawal even as a troop surge of about 30,000 soldiers and support personnel attempts to quell violence. The war is now in its fifth year.

“I don’t like it, I wish the boys would come home,” said Sharron Moser, 69, a retired utility-company supervisor from Stateline, Pa., who came to Bush’s speech. “I think it’s been going on long enough. The people over there should be able to defend themselves by now.”

The 167th Airlift Wing of the Air National Guard in Martinsburg has sent troops to Iraq and Afghanistan, and Bush cited several soldiers who have gone on multiple deployments in those wars. Mr. Bush likened the Qaeda threat in Iraq to that faced by American troops in Afghanistan. Mr. Bush said Al Qaeda seeks to destabilize the government and establish a “safe haven” in Iraq as it did in Afghanistan.

“We must win it, we must succeed for our own sake. We must defeat Al Qaeda in Iraq,” Mr. Bush said. “Victory in this struggle will require more patience, more courage, and more sacrifice.”

The president yesterday spoke with Iraqi Prime Minister al-Maliki, urging him to focus on combating Al Qaeda, securing Iraq’s borders, building political support and improving Iraqi security forces, spokesman Tony Snow said.

Increased political pressure may force Mr. Bush to begin withdrawing American troops from Iraq later this year, according to Senator Levin, the head of the Armed Services Committee. Democrats plan further attempts to reduce troops in military spending plans to be considered after the July 4 recess.

“The momentum is there” for change in Iraq, Mr. Levin said in a June 29 interview.