(Adds Bush quotes, White House spokesman, background)

By Matt Spetalnick

WASHINGTON, Feb 13 (Reuters) - U.S. President George W. Bush ordered expanded financial sanctions on Wednesday against senior Syrian officials and their associates in his latest bid to step up pressure on Damascus.

The measures are intended to freeze U.S. assets of those believed responsible for actions that "undermine efforts to stabilize Iraq" or have benefited from public corruption in Syria, the White House said.

Bush also reasserted U.S. accusations that Syria was meddling in neighboring Lebanon and fomenting problems for Beirut's pro-Western government.

"I wish to emphasize ... my ongoing concern over the destabilizing role Syria continues to play in Lebanon, including its efforts to obstruct, through intimidation and violence, Lebanon's democratic processes," Bush said in a statement.

Damascus has repeatedly denied the allegations by Washington, which has long tried to isolate Syria diplomatically.

Syrian forces ended a 29-year presence in Lebanon under international pressure after the 2005 assassination of former Lebanese premier Rafik al-Hariri, but the United States says Syria has continued to interfere in Lebanon.

Washington imposed economic sanctions on Syria in 2004, mainly over its support for the Lebanese guerrilla group Hezbollah and the Palestinian militant group Hamas. It has since blacklisted several Syrian officials.

The U.S. Treasury Department in November imposed sanctions against four people it said were linked to Syrian efforts to undermine Lebanon's sovereignty, including a general dealing with security and a cousin of Syrian President Bashar al-Assad. Damascus dismissed those U.S. measures as "pitiful."

Bush's latest order expanding sanctions on Syrian officials and their associates did not name names. The White House said the list was still being finalized.

U.S. commanders have acknowledged that Syria has stepped up efforts to restrict the flow of militants across its border into Iraq, where U.S. forces are nearing the five-year mark since an invasion that toppled Saddam Hussein.

But U.S. officials say Damascus must take further action.

"While the Syrian Government has taken some steps against terrorists aimed at ensuring Syria's internal stability, Syria remains the primary route for terrorists crossing into Iraq," White House spokesman Gordon Johndroe said.

"There are many verifiable actions Syria could take in this regard -- such as strengthening its visa requirements -- that would demonstrate a willingness to assist the efforts of the Iraqi government and the international community to stabilize Iraq," he added. (Editing by Eric Beech)

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