MEXICO CITY — As the U.S. and Mexican governments increasingly target the brutal criminal gang known as Los Zetas, questions are being asked about why law enforcement officials don't seem to be paying equal attention to an older and larger cartel that's the largest provider of illegal drugs smuggled into the United States.

Public security analysts say a view has spread among some Mexicans that President Felipe Calderon is soft on the Sinaloa Cartel. And now a court filing by an accused kingpin in U.S. federal court has suggested that the Obama administration, too, is negotiating with the Sinaloa Cartel even as it ratchets up pressure on the rival Zetas.

Experts in Mexico City and Washington say the issue is as much about public opinion in the run-up to Mexico's 2012 presidential elections as it is about efforts to reduce the violence that's killed some 40,000 people in Mexico since 2006.

"The perception that people have of the government not going after the Sinaloa Cartel is undermining its credibility," said Alberto Islas, a security analyst with Risk Evaluation Ltd., noting that the group's leaders "are the biggest smugglers of cocaine, meth and heroin into the U.S."

The Zetas, led by deserters from the Mexican army, got their start in the late 1990s as an enforcement arm of the Gulf Cartel along Mexico's border with Texas. They've since struck out on their own, dismembering their rivals — sometimes literally — and engaging in extortion, kidnapping and human trafficking as well as narcotics smuggling.

In contrast, the Sinaloa Cartel, which U.S. officials say provides about 25 percent of the illegal drugs smuggled into the United States, generally favors bribing high government officials over the brutality Los Zetas employ to protect their smuggling routes, experts say.

On July 25, the White House issued an executive order naming four groups around the world as transnational criminal threats. Along with Los Zetas, the order named the Yakuza of Japan, the Camorra of Italy and the Brothers' Circle, which operates from countries that once composed the Soviet Union.

The order said the four groups were involved in a "wide variety" of criminal activity that included weapons trafficking, piracy and complex financial fraud.

Rafael Lemaitre, a spokesman for the White House Office of National Drug Control Policy, said the order didn't include the Sinaloa Cartel because its activities were limited primarily to drug trafficking, while the Zetas had branched into a "variety" of other crimes.

"We already have a robust sanction regime" — the Kingpin Act — "that targets organized (criminal groups) that engage mostly in drug trafficking, such as Sinaloa," he said.

Other descriptions make it clear, however, that the Sinaloa Cartel is a huge criminal syndicate.

"The cartel functions like a transnational firm, with operations in over 40 countries," U.S. Attorney Laura E. Duffy of the southern district of California told the Senate drug caucus June 15. "Its reach is believed to extend across the Pacific to Australia and Japan and across the Atlantic to Eastern Europe, Italy, Portugal, Spain, Germany and several African nations."

Some experts said the Zetas were deserving of such targeting because they used mass killings so widely. That fuels a sense that the gangsters are unstoppable. With a reduction in the violence, citizens gain faith that authorities can reassert control.