* Arrests take Mexico's drug war inside crowded prisons
* Country counts 22 jailbreaks, dozens of riots this year
By Miguel Angel Gutierrez
MEXICO CITY, June 2 (Reuters) - The rounding up of thousands of suspects in Mexico's drug war has left the already unruly prison system overwhelmed with jailbreaks and struggling to contain deadly riots between inmates from rival gangs.
Dozens of violent clashes have rocked jails this year and a stream of inmates have escaped. Last month drug hitmen dressed as police screeched up to a northern Mexico prison in a convoy of vans and freed 53 prisoners who were seen on security cameras pouring into the street.
The chaos is posing another security risk for President Felipe Calderon, who has made crushing drug violence the centerpiece of his presidency.
Mexican media count 22 jailbreaks this year and some 40 prison feuds, fueled by guns smuggled in by visitors and lax or corrupt guards who let prostitution and drug peddling go on within prison complexes.
April alone saw 19 riots in jails in Mexico City, where wealthy inmates bribe guards for spacious cells with televisions, while others sleep on bare floors in crowded conditions, Mexico's Human Rights Commission says.
Guards have made inmates strip naked and lie down in lines in prison courtyards as they attempt to restore order.
"We have a flashpoint with corruption, huge overcrowding, extortions and things going in that shouldn't," Patricio Patino, deputy head of the federal prison service, told Mexican radio.
Soldiers and police have rounded up some 40,000 drug gang suspects since Calderon launched his army-led drug crackdown in late 2006, earning praise from Washington and scoring points with voters fed up with years of Mexico being used as a route for trafficking South American cocaine to the United States.
But rights activists say the overcrowding makes prisons fertile ground for corruption.
"The actions of criminal gangs move into the prisons once their members are captured," Andres Calero, a Mexican human rights commissioner, told Reuters.
NEW JAILS BEING BUILT
Twenty prisoners died in March in a riot in a new prison outside the violent border city of Ciudad Juarez. In October, a jail feud killed 21 inmates in the border city of Reynosa.
In February hitmen burst into another northern jail, freeing nine inmates and killing and burning the bodies of three others.
Mexico's drug war has killed some 2,500 people so far this year, apace with 6,300 drug-related deaths in all of 2008.
A spillover of violence into U.S. border states like Arizona and California is worrying President Barack Obama, who visited Mexico in April to pledge support for the drug war.
U.S. officials say a long-promised $1.4 billion drug aid package will help modernize Mexico's prison system.
Ricardo Najera, spokesman for Mexico's attorney general's office, said the first of three maximum-security prisons being built in southern Mexico could be ready by next year.
"They are going to take some of the pressure off," he said.
Public Security Minister Genaro Garcia Luna said on Tuesday that a dozen additional prisons, built and run by private companies, would be ready to hold Mexico's top criminals by 2011.
Mexico's most embarrassing prison break was the 2001 escape of top drug kingpin Joaquin "Shorty" Guzman from a maximum-security facility in a laundry van after he paid off guards.
Guzman, head a powerful cartel from the northwestern state of Sinaloa, then started a war against rivals and the army that is stoking much of the new violence in Mexico.
Even before the spate of drug arrests, Mexico's prisons were famously unruly places where money rules and drug lords can run smuggling rings from their cells by mobile phone.
In Tijuana, jails are filled to three times their capacity and nearby buildings get pelted with rocks and bottles by inmates who battle over food, drugs and prostitutes. (Additional reporting by Lizbeth Diaz in Tijuana; Writing by Robin Emmott; Editing by Catherine Bremer and Xavier Briand)