SAN'A, Yemen -- Corruption, an inefficient security force and an intoxicating plant that keeps most men in Yemen high for up to six hours a day all stand in the way of America's battle against Al Qaeda's Yemen wing, which is believed responsible for a plot to mail bombs to the United States.

The plot to send parcels packed with explosives to two Chicago-area synagogues underlined the creativity of the Yemen-based militants as they try to penetrate the West's anti-terror defenses, taking advantage of a culture of impunity at home as well as the relatively relaxed security on cargo flights. The terror network has in the past largely targeted commercial flights, including a failed Christmas Day attempt to blow up a passenger jet as it landed in Detroit.

"This is a whole new approach. We haven't seen Al Qaeda resort to this kind of tactic," said Riad Kahwaji, head of the Institute for Near East and Gulf Military Analysis, a Dubai-based think tank. "On the Yemeni side, they'll have a lot to answer for to regain their credibility."

Yemeni authorities smarted at the criticism and announced they had arrested a woman and were searching for other Al Qaeda linked suspects. Investigators also checked some two dozen other suspicious packages in the capital, San'a, and questioned cargo workers at the city's international airport as well as employees of the local shipping companies contracted to work with FedEx and UPS.

"We guarantee the determination of Yemen in confronting and combating terrorism," Yemeni President Ali Abdullah Saleh said Saturday at a press conference.

But life in San'a reflects some of the challenges faced by anyone trying to isolate and ultimately destroy a terror group that uses religion as both ideology and for recruitment.

Women in public wear flowing black robes and cover their heads except for a narrow slit for the eyes. Many of the men are bearded, a hallmark of piety, and in robes with an ornamental dagger tucked in a belt.

Many stores close during Islamic prayer times, which are announced by the shrieking voices of hundreds of muezzins echoing across the city.

Weapons are everywhere, with some estimates claiming that Yemenis hold about 50 million firearms ranging from city dwellers with AK-47 assault rifles to tribesmen in rural areas with rocket-propelled grenades, heavy machine-guns and mortars that they use at will against security forces or in tribal feuds.

Cinemas in San'a, the capital, have signs outside them warning patrons against bringing weapons into the auditorium.

Enter the United States, which has for nearly a year waged a war against Al Qaeda militants who have been building up their presence in Yemen for several years. The insurgents find refuge with tribes in remote mountain ranges where the central government has little control and draw sympathy, or support in some cases, from a population of some 23 million known for its religious fundamentalism and disdain for America because of the wars in Iraq and Afghanistan.

Some 50 elite U.S. military experts are in Yemen training its counterterrorism forces and Washington is giving $150 million in military assistance to Yemen this year for helicopters, planes and other equipment. A similar amount is given for humanitarian causes.

But there's been little sign of progress as the government is torn between U.S. pressure to fight the militants and its need for support from the unruly tribes that harbor the extremists.

Security officials say most government forces deployed in provinces where Al Qaeda militants are known to be hiding are there primarily to protect oil installations and show no willingness to fight. In some cases, said the officials, army commanders ignore known members of Al Qaeda pretending to be tribesmen practicing at makeshift shooting ranges.

The officials, who agreed to discuss the level of readiness by the forces only in exchange for anonymity, said the troops also suffer from lack of discipline and conviction.

Many units, the officials said, are poorly equipped because most of the modern arms and hardware donated by the United States and other Western nations go to elite units led by the president's close family members, which are primarily tasked with protecting Saleh's 32-year rule against rivals -- not fighting Al Qaeda.

The country also faces an armed Shiite insurgency in the north, and the army suffered heavy casualties and saw dozens of soldiers captured during fighting there earlier this year because of the poor state of the armed forces.

The habit of chewing qat, a plant with a mild amphetamine-like stimulant, is another example of the challenges faced by Washington in Yemen.

An estimated 60 percent to 70 percent of Yemen's adult males are thought to be qat users, which in effect means that they are high on the green leafy plant from 1 p.m. to early evening every day.

The military is no exception, and the security officials say that undermines discipline and renders soldiers unfit to perform combat duties for a big part of the day.

Military personnel are forbidden to chew qat while on duty, but the ban is widely ignored in barracks as well as security checkpoints in rural areas.

Many say things are done differently in Yemen and the United States should let the government fight Al Qaeda in its own way.

"If left alone, we can deal with Al Qaeda with sustained and patient police work," said Abdul-Ghani al-Iryani, a political analyst from one of Yemen's most powerful families. "The number of core Al Qaeda fighters is small, but when you send an army to pursue 15 of them, they tend to double their number before the army leaves."