(Adds dropped word "blow" in 7th paragraph)

By Caren Bohan

SAN ANTONIO, Texas, March 5 (Reuters) - Hillary Clinton's attacks on Barack Obama's lack of foreign policy experience provide a model for how Republicans could run against Obama if he becomes the Democratic candidate for U.S. president.

Clinton's attacks, which helped her win Ohio, Texas and Rhode Island on Tuesday in the state-by-state battle for the party nomination, exposed a vulnerability for Obama, who has served only three years in the Senate representing Illinois.

John McCain, who wrapped up the Republican nomination for the November election, is already highlighting his seasoning on national security and would likely assert that Obama is not tough enough to keep America safe.

This was a tactic fellow Republican George W. Bush used in his 2004 re-election campaign against Democrat John Kerry.

"Certainly, McCain will go after Obama's inexperience on foreign policy," said Bruce Buchanan, a political scientist at the University of Texas, Austin.

Obama still has the edge in gaining the Democratic presidential nomination but the race is expected to continue for at least six more weeks, further helping McCain.

Clinton, a New York senator, who would be the country's first woman president, struck her deadliest blow launching an aggressive ad campaign last week suggesting Obama was not ready to lead on national security.

CLINTON SAYS SHE'S "TESTED"

The ad featured a phone ringing at the White House as a narrator ominously warns: "It's 3 a.m. and your children are safe and asleep. But there is a phone in the White House and its ringing. Something is happening in the world."

The voice then asks whether the person taking the call is "tested and ready to lead in a dangerous world."

Clinton at the same time launched an attack on Obama for what she called his inconsistencies on international trade.

"It does seem as if Obama's momentum in the polls was arrested by those twin issues -- national security and trade," said Dante Scala, a University of New Hampshire political scientist.

Arizona Sen. John McCain, a former prisoner of war in Vietnam, has had a high-profile on foreign affairs debates in Washington for decades.

Apart from raising the experience question, Buchanan said McCain would argue that Obama's plan to begin an immediate phased withdrawal of U.S. forces from Iraq amounted to "cutting and running."

The strategy worked for Bush four years ago even though he faced a decorated Vietnam veteran in Kerry. Bush painted his opponent as a "flip-flopper" lacking the toughness to face America's enemies.

HITS BACK

Analysts said McCain would find it easier than Clinton to highlight Obama's relative thin national security resume.

Clinton's own claim to be "tested and ready" relies heavily on her years as first lady when her husband Bill Clinton was president. Not all voters view that as real experience.

Obama has hit back at Clinton, contrasting his early opposition to the Iraq war with her 2002 Senate vote to authorize it. Both now favor withdrawing the troops, a policy which has popular support.

Mike Green, an analyst at the Center for Strategic and International Studies, said Clinton and Obama may differ to some degree on tactics but they are not far apart on foreign policy substance.

"In the general election you will see some very stark differences in policy," said Green, a former White House official who has advised McCain but emphasized he was not speaking on behalf of the campaign.

Green said Obama would also face criticism for suggesting that as U.S. president he would try to talk directly with foes such as Iranian President Mahmoud Ahmadinejad, who often speaks about the destruction of Israel and rejects international calls to rein in its nuclear program. (Writing by Caren Bohan; Editing by Alan Elsner and David Storey)

AlertNet news is provided by