BAGHDAD (AP) – Suicide bombers and militiamen fought back ferociously in the seventh week of the Baghdad security crackdown, killing at least 508 people in the past six days, but the government vowed Friday it would win the race against terrorism and despair.

As the deadly week drew to an end on the Muslim day of rest and prayer, radical cleric Muqtada al-Sadr blamed the United States for the violence and called for a huge anti-American demonstration April 9, the fourth anniversary of the fall of Baghdad.

Marketplaces in Baghdad, Tal Afar and Khalis stood in ruins. Clean up crews shoveled broken glass and debris into wheelbarrows in bloodstained streets. Bomb victims in wooden coffins were hoisted atop cars and vans for the trip south for burial in the Shiite holy city of Najaf.

In a sign of how deeply officials were shaken by the carnage, a top aide to Prime Minister Prime Minister Nouri al-Maliki, Sami al-Askari, pledged that the government would not relent in efforts to curb violence.

“There is a race between the government and the terrorists who are trying to make people reach the level of despair,” al-Askari said. “But the government is doing its best to defeat terrorists and it definitely will not be affected by these bombings.”

The new U.S. commander in Iraq, Gen. David Petraeus, issued a statement blaming al-Qaida in Iraq for the week’s first major suicide attack, a twin truck bombing that killed 80 people and wounded 185 at markets in Tal Afar in the far northwest of the country.

He said al-Qaida’s leaders “once again displayed their total disregard for hum an life, carrying out barbaric actions against innocent Iraqi citizens in an effort to re-ignite sectarian violence and to undermine recent Iraqi and coalition successes in improving security in Baghdad.”

The Pentagon ratcheted up its rhetoric against Iraq’s Sunni Arab insurgents as well, condemning the recent use of chlorine gas as a weapon. It called that the first use of a poison gas against Iraqis since Saddam Hussein ordered mustard gas attacks on ethnic Kurds in northern Iraq nearly 20 years ago.

Maj. Gen. Michael Barbero, a deputy operations director on the Joint Staff, said he was not implying the insurgents were following Saddam’s pursuit of weapons of mass destruction. But his comments recalled a key U.S. argument for invading Iraq – Saddam’s history of using chemical weapons against his own people.

Insurgents in their Anbar province stronghold have carried out or unsuccessfully launched at least eight attacks using toxic chlorine gas since Jan. 28, when 16 people were killed in Ramadi, the provincial capital.

While Bush, the American military and U.S. diplomats in Iraq have expressed cautious optimism about the crackdown on violence that began Feb. 14 in Baghdad, Anbar province and regions surrounding the capital, the ease with which suspected al-Qaida suicide bombers have continued striking Shiite targets must be deeply disconcerting.

Only about a third of the additional 30,000 soldiers and Marines that Bush pledged for the security drive are in the country, with the full deployment not expected until June.

Al-Sadr’s statement was his first since March 16, when he urged supporters to resist U.S. forces through peaceful means. U.S. and Iraqi officials say al-Sadr remains in Iran, sitting out the security crackdown, but aides have told The Associated Press he has returned to Najaf.

His latest declaration was read to worshippers during Friday prayers at a mosque in Kufa, a twin-city to Najaf where al-Sadr frequently led the ritual, and in Baghdad’s Sadr City Shiite enclave.

“I renew my call for the occupier to leave our land,” he said in the statement, a copy of which was obtained by AP. “The departure of the occupier will mean stability for Iraq, victory for Islam and peace and defeat for terrorism and infidels.”

Al-Sadr, whose Mahdi Army militiamen fought American troops in 2004 but have generally cooperated with the current U.S.-Iraqi security push in Baghdad, blamed the presence of U.S. forces in Iraq for the rising violence, lack of services and sectarian bloodshed.

“You, oppressed people of Iraq, let the entire world hear your voice that you reject occupation, destruction and terrorism,” he said in calling for the April 9 demonstration.

The U.S. military said one soldier was killed and a second wounded Thursday during a patrol in southern Baghdad, raising to at least 3,245 the number of American military personnel who have died since the war began in 2003, according to an AP count.

Iraqi police said 26 people were slain or found dead nationwide Friday, a huge drop from the 181 killed Thursday, most in suicide attacks on markets in Khalis, 50 miles north of Baghdad, and the Shaab neighborhood in the capital’s north.

A key representative of Iraq’s most revered Shiite cleric, whose word is law with many members of the majority sect, may have condemned to defeat a key piece of reconciliation legislation proposed by the Shiite prime minister – a measure insisted on by his U.S. backers.

Criticizing a draft law that would allow many members of Saddam’s former Baath Party to regain their government jobs or begin drawing pensions, Sheik Abdul Mahdi Al-Karbalai warned “valiant brothers in parliament must be cautious and alert” when taking up the measure.

He said the proposal “could give criminal individuals from the security agencies of the former regime a loophole that allows them to return to important jobs.”

Al-Karbalai’s Friday sermons at the Imam Hussein mosque in Karbala reflect the thinking of Grand Ayatollah Ali al-Sistani, the country’s most revered Shiite cleric.

The Bush administration has set out four benchmarks for al-Maliki’s government. One is passage of the de-Baathification law as a way to reconcile with Sunni insurgents.

Aides say al-Maliki has been warned by U.S. officials they will withdraw support for his shaky government if that proposal and three others – one on fair distribution of oil revenues, one setting a date for regional elections and several constitutional amendments – aren’t passed in parliament by June 30. All four would benefit the Sunni minority that ruled over the oppressed Shiite majority for decades.

Washington denies linking support for al-Maliki with those measures, but has declared it is using them to measure his commitment to curbing violence and establishing the rule of law.

AP-ES-03-30-07 1707EDT