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.

"For a long time, the government has been in denial that the violence has been a problem," said Vanda Felbab-Brown, a security expert at the Brookings Institution, a research center in Washington.

But appearing to let crime groups that seem less prone to violence get a pass also causes problems.

"It's politically sensitive, because people start to say that by prioritizing the most violent group, there is corruption and favoritism," Felbab-Brown said.

Calderon's administration denies that it goes any easier on the Sinaloa Cartel.

"The battle against all organizations must be done in a systematic way," national security spokesman Alejandro Poire said last week. "I emphasize: Peace cannot be achieved by allowing some criminal organizations to flourish."

The suggestion that the United States also deals less harshly with the Sinaloa Cartel comes largely from court filings in the case of Vicente Zambada-Niebla, the son of an alleged Sinaloa kingpin, whom Mexico extradited to stand trial in Illinois on narcotics charges. In court papers, he's alleged that before his March 2009 arrest he served as an informant for U.S. Drug Enforcement Administration agents operating in Mexico.

In a court filing July 29, his lawyer said U.S. prosecutors had dropped narcotics charges against a lawyer and confidant of the Sinaloa Cartel, Humberto Loya Castro, in December 2008 as part of a pact with its bosses to offer dirt on rival traffickers.

The court filing charged "that the United States has a policy of entering into agreements with individuals who they know are violent narcotics traffickers, so long as those persons are willing to provide information against other drug traffickers, and that they entered into such an agreement with the leadership of the Sinaloa Cartel."

Felbab-Brown, while not commenting directly on the court case, said arrests in Mexico often resulted from crime groups providing information on their enemies.

"It's other drug-trafficking groups ratting on each other. A lot of the intel comes this way," she said.