By KAREEM FAHIM and RICK GLADSTONE

Published: December 26, 2012

BEIRUT, Lebanon — Syria’s government suffered an embarrassing new setback as the top general responsible for preventing defections within the military became a defector himself, making what insurgents described on Wednesday as a daring back-roads escape by motorcycle across the border into Turkey.

The defector, Maj. Gen. Abdul Aziz Jassem al-Shallal, the chief of the military police, was one of the highest-ranking military officers to abandon President Bashar al-Assad in the nearly two-year-old uprising against him.

His departure, first reported by Al Arabiya late on Tuesday evening and confirmed by opposition figures on Wednesday, came as a flurry of diplomatic activity suggested the possibility of movement toward a political solution to the Syrian crisis. A deputy Syrian foreign minister flew to Moscow for meetings with Kremlin officials, and the international envoy who met with Mr. Assad in Damascus earlier this week was planning to visit Moscow this weekend. Russia, one of Mr. Assad’s most ardent foreign defenders, has in recent weeks suggested it was open to a negotiated transition that would ease him out of power.

Opposition figures said General Shallal’s defection had taken weeks to prepare and ended with a four-hour sprint by motorcycle to the Turkish border, driving through woods and on muddy roads. In a video broadcast by Al Arabiya, the general said that he had taken the step because the Syrian military had deviated from its mission to protect the country, and had transformed into “a gang for killing and destruction.”

“The regime army has lost control over most of the country,” the general said in an interview on the Saudi-owned channel, which has heavily criticized the Syrian government.

Opposition fighters embraced the defection as more than a symbolic blow to the government because of the general’s primary responsibility as an enforcer of Mr. Assad’s repression of dissent and guarantor of loyalty by the armed forces. As head of the military police, General Shallal was responsible for the department that was supposed to stop defections. He also presided over a force that guarded prisons where civilian dissidents were held.

Maj. Ibrahim Moutawe, who defected from the Syrian Army a year ago, said defection was a “last resort” for high-ranking officials like General Shallal. “They only consider it when fear and danger begin to threaten them directly, and when the regime can no longer protect them,” he said.

General Shallal was not a member of Mr. Assad’s inner circle, and analysts said that the defections of other officials with impressive titles — including the prime minister, a brigadier general and a well-known government spokesman — had done little to shake Mr. Assad’s basic hold on power.

More critically, the opposition has failed to attract either officers or rank-and-file soldiers belonging to Syria’s Alawite minority, the sect that Mr. Assad belongs to, doing little to assuage fears among Alawites that the Sunni-led insurgency threatens their existence, analysts said.

But the departure of a major general who publicly condemned the armed forces seemed likely to undercut Mr. Assad’s attempts to maintain morale.

The negotiations for the general’s defection began weeks ago, after members of his tribe reached out to opposition commanders, according to Louay Mekdad, the political and media coordinator for the Free Syrian Army, an umbrella organization for rebel fighting groups. Mr. Mekdad said that the general had tried to defect several times before, but had been prevented for what he called “technical reasons,” without giving any more detail.

Rebel commanders gave differing accounts of how much power the general had held in Syria. One commander said he had been a member of Mr. Assad’s “crisis team” of top military, security and intelligence officials coordinating the government’s response to the war. Capt. Adnan Dayoub, a rebel commander in Hama, said that General Shallal had been responsible for prisons — “God knows how many,” he said — and was almost certainly guilty of crimes.

“He’s contaminated from top to bottom,” the captain said. “Tomorrow he will be a hero.”

Another commander said General Shallal and many other top military leaders had been stripped of power during the last two years, and served as figureheads. One Syrian security official was quoted by Reuters as saying the general had been near retirement when he defected.

Among civilians who have abandoned Mr. Assad, the highest-ranking defector so far has been the prime minister, Riyad Farid Hijab, who fled to Jordan on Aug. 6. In the past few weeks, unconfirmed reports have also abounded about the possible defection of Syria’s Foreign Ministry spokesman, Jihad Makdissi, who had numerous foreign contacts and who disappeared from public view in early December.

The Guardian reported this week that Mr. Makdissi had fled to the United States and was cooperating with American intelligence. But Patrick Ventrell, a State Department spokesman in Washington, said Wednesday that Mr. Makdissi was not in the United States.

Mr. Makdissi’s whereabouts and status remained murky. American officials said that they did not know where he was, and that reports this month saying that Mr. Makdissi had flown to London were incorrect.

In Lebanon, Syria’s interior minister, Muhammad Ibrahim al-Shaar, who had been recovering at a Beirut hospital from wounds said to have been received in a Dec. 12 suicide bombing outside his offices in Damascus, was on his way back to the Syrian capital on Wednesday, according to a Lebanese security official.

In a sign of the growing pressure on top Syrian officials, a Lebanese security official was quoted by The Associated Press as saying that Mr. Shaar had left the hospital abruptly for fear of arrest in Lebanon, after the authorities received information of a possible international warrant against him for his role in suppressing the Syrian uprising.

Against the backdrop of the Assad government’s growing isolation, Russia appeared to be playing a more active diplomatic role. An official from Russia’s Foreign Ministry was quoted by the Itar-Tass news service as saying that a Syrian government delegation would meet Thursday with Russia’s foreign minister, Sergey V. Lavrov. That will be followed on Saturday by a visit from the special representative from the United Nations and Arab League, Lakhdar Brahimi, who has been in Syria this week.

Mr. Brahimi is widely believed to have presented Mr. Assad with a proposal that would allow him to remain in his post for a specified amount of time, but require him to transfer his authority to a transitional government.

Russia has staunchly opposed military intervention in Syria, insisting on a negotiated solution. But its officials have acknowledged that Mr. Assad’s forces are losing control, and are preparing for a chaotic period of transition.

Fyodor Lukyanov, a top analyst, said Russia would be eager for a solution that imposed a political process and ruled out “regime change by force.” Any formulation that allowed Mr. Assad to remain until the end of his term in 2014 — and especially one that put the choice into the hands of Syrian voters — would be seen in Russia as a “very, very good solution,” said Mr. Lukyanov, editor of Russia in Global Affairs.

Kommersant, a respected daily newspaper, reported that the sticking point in Mr. Brahimi’s proposal is whether Mr. Assad would retain the right to run for office again when his presidential term ends. The newspaper reported that Mr. Assad insists on retaining that right.

Kommersant also reported that Russia and the United States had discussed the question of asylum for Mr. Assad, mentioning specifically the United Arab Emirates, Belarus or Venezuela.

Mr. Lavrov has said Russia will not pressure the Syrian leader to leave. “We don’t get involved in regime change,” he told Russia Today, a cable news channel.

Kareem Fahim reported from Beirut, and Rick Gladstone from New York. Reporting was contributed by Hwaida Saad from Beirut, Ellen Barry from Moscow, Hala Droubi from Dubai, United Arab Emirates, and Eric Schmitt from Washington.