Washington, Apr 11: President George W. Bush said would suspend US troop withdrawals from Iraq this summer but tried to reassure a weary public that the war, to be handed to his successor in January, was "not endless."

Bush also cut the length of tours of duty to one year from 15 months for troops deploying to Iraq and Afghanistan starting on Aug. 1 to try to ease strains on the military.

He endorsed a recommendation by his commander in Iraq, Gen. David Petraeus, to complete a withdrawal in July of about 20,000 extra combat forces deployed in the last year but then impose a 45-day freeze on the remaining 140,000 troops to assess the security situation before considering more cuts.

"I've told him he'll have all the time he needs," Bush said in a televised speech at the White House.

He stepped up his criticism of Iran, accusing it of backing militants who conduct attacks in Iraq, and warned that failure in Iraq would embolden both Iran and al Qaeda.

"Iraq is the convergence point for two of the greatest threats to America in this new century: al Qaeda and Iran," Bush said.

Petraeus had told a contentious congressional debate on the costly and unpopular war this week that progress was "fragile and reversible" and a renewed outbreak of violence has left 20 American troops dead so far in April.

The Iraq war, now in its sixth year, has again become a major issue in the campaign for the U.S. presidential and congressional elections in November, with Democrats accusing the Bush administration of not having an exit strategy.

"There is no end in sight under the Bush policy. It is time to bring this war in Iraq to a close," Democratic presidential candidate Barack Obama said at a rally in Gary, Indiana.

Hillary Clinton, the other Democratic contender for president, said: "Our troops have done all that's been asked of them and more. It's time for the president to answer the question being asked of him: In the wake of the failed surge, what is the endgame in Iraq?"

Bush defended his war policies and said succeeding in Iraq was crucial for U.S. security interests.

"And while this war is difficult, it is not endless," he said.

Bush said progress was being made in Iraq and that his "surge" of U.S. troops in the last year had helped renew the prospects of success. Serious and complex challenges remain in Iraq, from the presence of al Qaeda to the destructive influence of Iran, to hard compromises needed for further political progress. Yet with the surge, a major strategic shift has occurred," Bush said.