* Quijano says to go to Supreme Court if vote not recounted
* About 2,000 supporters march on electoral tribunal's hotel
* Leftist winner of vote would be first ex-rebel president
By Noe Torres
SAN SALVADOR, March 11 (Reuters) - The runner-up in El Salvador's presidential election asked the electoral tribunal on Tuesday to annul the tight contest and threatened to go to the Supreme Court if necessary.
Norman Quijano of the right-wing Nationalist Republican Alliance (Arena) trailed Salvador Sanchez Ceren of the ruling leftist Farabundo Marti National Liberation Front in Sunday's vote by 0.22 percentage points, or fewer than 7,000 votes.
On Tuesday, about 2,000 Quijano supporters waving red, white and blue Arena party flags marched to barricades in streets around the hotel where the tribunal is counting the votes.
"We cannot allow such a blatant fraud," said Prudencia Aparicio, a 25-year-old owner of a cake shop.
The tribunal is checking that records from polling stations match electronic tallies from a preliminary count on Sunday night, but not recounting individual votes.
It called the outcome "irreversible" on Monday, but Quijano declared himself the real winner, and the stand-off is raising concerns of a possibly protracted dispute.
"WE HAVE BEEN ROBBED"
After Arena filed a petition with the tribunal, Quijano said that he doubted the electoral authority would accept his challenge and that he would probably have to take his complaint to El Salvador's Supreme Court.
"We estimate that we have been robbed by between 30,000 and 40,000 votes," he told Reuters.
Arena demanded a vote-by-vote recount, a step that the tribunal said was not allowed under the country's electoral law.
Sanchez Ceren, a former commander of rebel forces in El Salvador's civil war, said on Monday that he expected he could be declared winner by Thursday, which would make him the first ex-rebel leader to become president.
The war claimed 75,000 lives and left the country deeply divided after leftist insurgents battled a string of U.S.-backed right-wing governments between 1980 and 1992.
Sanchez Ceren has promised to make a "national pact" with conservative parties and business owners, and to establish a moderate government.
Quijano has argued Sanchez Ceren would steer the country to the far left and bow to the influence of socialist Venezuela.
Fernando Arguello, a member of the electoral court, said that the body was unlikely to declare a winner until Quijano's demand to annul the election had been resolved.
But, he said, "We can't wait much longer because the country doesn't deserve for this process to be drawn out."