(Edits, adds US intelligence assessment)
* Attack on TV station south of Damascus
* "We are in a war" says Assad
* U.S. sees Assad holding firm, digging in
By Oliver Holmes
BEIRUT, June 27 (Reuters) - Gunmen stormed a pro-government Syrian TV channel headquarters on Wednesday, bombing buildings and shooting dead three employees, state media said, in one of the boldest attacks yet on a symbol of the authoritarian state.
President Bashar al-Assad declared late on Tuesday that his country was "at war". U.S. intelligence officials said the Syrian regime was "holding fairly firm" and digging in for a long struggle against rebel forces who are getting stronger.
The dawn attack on Ikhbariya television's offices, located 20 km (15 miles) south of the capital, as well as overnight fighting on the outskirts of Damascus showed 16 months of violence now rapidly encroaching on the capital.
Ikhbariya resumed broadcasting shortly after the attack, displaying bullet holes in its two-storey concrete building and pools of blood on the floor. One building had been almost completely destroyed.
"I heard a small explosion then a huge explosion and gunmen ran in. They ransacked the offices and entirely destroyed the newsroom," an employee who works at the offices in the town of Drousha told state media at the scene.
The Syrian media are tightly regulated by the Ministry of Information. Although Ikhbariya is privately owned, opponents of Assad say it is a government mouthpiece.
SYRIA "AT WAR"
During the pro-democracy revolt against the Assad family's four-decade rule, Ikhbariya has been pushing to counter what it says is a campaign of misinformation by Western and Arab satellite channels on the uprising that began in March 2011.
"We live in a real state of war from all angles," Assad told a cabinet he appointed on Tuesday, in a speech broadcast on state television. "When we are in a war, all policies and all sides and all sectors need to be directed at winning this war."
The declaration marks a change of rhetoric from Assad, who had long dismissed the uprising against him as the work of scattered militants in "terrorist gangs" funded from abroad.
The rambling speech - Assad also commented on subjects as far afield as the benefits of renewable energy - left little room for compromise. He denounced the West, which "takes and never gives, and this has been proven at every stage".
The United Nations accuses Syrian forces of killing more than 10,000 people during the conflict, which began with a popular uprising and has built up into an armed insurgency against four decades of rule by Assad and his father.
DIGGING IN FOR LONG HAUL
Despite some military defections, mainly from low to mid-level ranks, Assad's inner circle remains cohesive and the war is still likely to be a drawn-out struggle, senior U.S. intelligence officials said, in an assessment dimming any U.S. hopes that Assad will fall soon of his own accord.
"Our overall assessment ... would be that we are still seeing the military regime forces fairly cohesive, they've learned some lessons over the last year and a half about how to deal with this kind of insurgency," an official said.
The insurgency is also getting stronger, he said.
"Both sides seem to be girding for a long struggle. Our sense is that the regime still believes it can ultimately prevail or at least appears determined to try to prevail and the opposition at the same time seems to be preparing for a long fight."
Despite the deterioration in Syria, so far there has been no sign of an appetite for Western intervention.
Video published by activists on Tuesday recorded gunfire and explosions in suburbs of Damascus. Syria's state news agency SANA said "armed terrorist groups" had blocked the old road from Damascus to Beirut on Tuesday.
The U.N. peacekeeping chief said it was too dangerous for a U.N. observer team, which suspended operations this month, to resume monitoring a ceasefire at the heart of a peace plan by international envoy Kofi Annan. The truce is in fact dead.
The Syrian Observatory for Human Rights, a group which compiles reports from rebels, said 135 people were killed on Tuesday, making it one of the bloodiest days of the conflict. The daily death toll in recent days has been about 100.
The observatory reported battles near the headquarters of the Republican Guard in Qudsiya, and in other Damascus suburbs of al-Hama and Mashrou' Dumar, just 9 km from the capital.
In neighbouring Turkey, Prime Minister Tayyip Erdogan ordered his armed forces to react to any threat from Syria near the border, after Syrian forces shot down a Turkish warplane on Friday off the Mediterranean coast.
NATO-member Turkey is the base for the rebel Free Syrian Army (FSA) and shelters 30,000 refugees. Rebel soldiers move regularly across the border and defectors muster inside Turkey.
(Additional reporting by Tabassum Zakaria in Washington. Editing by Douglas Hamilton and Jon Boyle)