* Assad's brother among Syrians on sanctions list
* White House calls on Assad to "change course now"
* Iran's Quds Force also targeted
* Some export licenses also canceled (Adds Clinton comments, paragraph 3)
By Mark Hosenball and Matt Spetalnick
WASHINGTON, April 29 (Reuters) - The United States slapped sanctions on Syria's intelligence agency and two relatives of President Bashar al-Assad on Friday in Washington's first concrete steps in response to a bloody crackdown on protests.
Assad, Syria's long-serving ruler, was not among those targeted under an order signed by President Barack Obama but could be named soon if violence by government forces against democracy protesters continued, a senior U.S. official said.
"The sanctions that were announced today are intended to show the Syrian government that its behavior and actions are going to be held to account," U.S. Secretary of State Hillary Clinton told reporters after a meeting with Japan's visiting foreign minister.
Sanctions for alleged human rights abuses were imposed against Maher al-Assad, Bashar's brother, and Atif Najib, one of his cousins, together with Syria's General Intelligence Directorate and its chief.
Iran's powerful Revolutionary Guard was also targeted, accused of helping Syria's crackdown. [ID:nLDE73R2FG]
The action, details of which were first reported by Reuters, marks a more assertive approach by Washington, which has been criticized by human rights groups for not doing more to curb Assad's efforts to crush an uprising against his autocratic 11-year rule.
But another U.S. official said the White House is "not ready" to call on Assad to step down -- as it has done with Libyan leader Muammar Gaddafi -- because Obama and his aides "do not want to get out in front of the Syrian people."
The White House said in a statement: "We call on President Assad to change course now, and heed the calls of his own people."
The sanctions, which include asset freezes and bans on U.S. business dealings for those on the list, build on broader U.S. measures against Syria in place since 2004.
There are questions, however, whether new sanctions against Assad's inner circle will have any dramatic impact since they are thought to hold few U.S. assets. But U.S. officials said they hoped European and Asian governments would follow suit.
"In addition to actions that we are taking, the United States believes that Syria's deplorable actions toward its people warrant a strong international response," White House spokesman Jay Carney said.
He welcomed the decision by the U.N. Human Rights Council to condemn Syria for its crackdown.
Separately, ambassadors from European Union nations discussed a package of possible economic sanctions which could be imposed on Syria to protest its violent crackdown on anti-government protesters.
Two Western diplomats told Reuters that the measures under discussion could include suspending work on a proposed free trade agreement between the EU and Syria and cutting off EU funding for Middle Eastern "cooperation" projects in Syria.
Washington has stepped up pressure but has still moved cautiously after working for the past two years to try to woo Damascus away from its alliance with U.S. foe Iran.
The Obama administration is also worried about stoking instability on U.S. ally Israel's borders and wants to avoid another military entanglement in the Muslim world, where it is involved in wars in Iraq and Afghanistan.
In his executive order, Obama said the Syrian government had committed "human rights abuses, including those related to the repression of the people in Syria, manifested most recently by the use of violence and torture.
A U.S. official said the new sanctions were meant to show that no member of the Syrian leadership was "immune" from being held accountable. "Bashar is very much on our radar and if this continues could be soon to follow," the official said.
"It puts Syria's leaders on notice that decisions to kill unarmed civilians have consequences," said Senate Foreign Relations Committee Chairman John Kerry.
A Syrian rights group said at least 500 civilians had been killed since the unrest broke out in Deraa on March 18. Authorities dispute the death toll, saying 78 security forces and 70 civilians died in violence they blame on armed groups.
Despite that, Obama's response to the Syrian crisis so far has been limited compared to Washington's role in a NATO-led air campaign against Gaddafi's forces in Libya and its call for his ouster.
Maher al-Assad is a brigade commander in the Syrian Army's 4th Armored Division that has played a key role in Deraa, where protesters have been killed by security forces, the White House said. Najib was described as former head of the Political Security Directorate for Deraa during the deadly crackdown.
The new sanctions also target the General Intelligence Directorate and its director, Ali Mamluk. The spy agency is accused by U.S. officials of repressing dissent and of involvement in the killing of protesters in Deraa.
The fifth target is Iran's Islamic Revolutionary Guard Corps - Quds Force, which is already under U.S. sanctions for supporting militant groups around the world.
The Quds Force, a branch of the Iranian government's principal security agency which operates outside Iran, is accused of being the "conduit" for material support Tehran has provided to Syrian authorities to suppress protests.
In addition, the U.S. Commerce Department revoked licenses for the export to Syria of parts for aircraft it said were used by senior members of the Syrian government. One of the licenses would have allowed the Syrians to obtain a luxury aircraft for Assad's use, U.S. officials said.
Obama also renewed Bush-era sanctions on Syria in effect since 2004, saying in a statement that while the Syrian government had reduced the number of foreign fighters bound for Iraq its actions and policies continued to pose a threat to U.S. national security and the economy. (Additional reporting by Tabassum Zakaria and Andrew Quinn; Editing by Eric Walsh)