An elaborate network of tunnels from Egypt has become the primary transport route for commercial goods entering the Gaza Strip, enabling the area's Hamas rulers to maintain a rudimentary economy in the face of an Israeli embargo.

Food products, machinery parts, raw materials and even antibiotics are delivered to Gaza through the tunnels, subject to fees from private families that own some of the passages and to taxes by Hamas. Other smuggled products range from cigarettes to mobile phones.

The traffic through the tunnels has enabled Gaza stores to begin slowly restocking shelves, which as recently as three months ago were without such basics as tea and underwear.

Israeli authorities, who say large quantities of weapons also are smuggled through the tunnels, are expected to press President Bush during his Middle East tour beginning today to demand that Egyptian President Hosni Mubarak do more to shut down the passages.

"The U.S. can engage with regional parties to strengthen border security and help the peace process," said Mark Regev, spokesman for Israeli Prime Minister Ehud Olmert. He estimated there are "dozens" of tunnels passing under the border on either side of the Rafah crossing to Egypt.

Hamas insists it has nothing to do with the tunnels. "Palestinians in Gaza are desperate, and desperate people resort to all means to survive," said spokesman Fawzi Barhoum. "Israel is using the issue to justify attacks against Hamas."

At least some of the tunnels have existed for years, used to smuggle products for sale on Gaza's black market. During the second intifada, the passages were used to bring in weapons, cash and people.

But the use of the tunnels has greatly expanded since June, when Israel responded to Hamas' forcible seizure of power in the Strip by imposing strict limits on the cross-border passage of goods.

An average of only 18 trucks per day are allowed to enter Gaza carrying food and humanitarian goods to sustain a population of 1.5 million, according to the United Nations. Only 19 trucksful of exports were allowed to exit between June and November.

Distributors and former Palestinian Authority intelligence officers in Gaza say Hamas, anxious to circumvent the embargo, has taken control of all activity through the tunnels.

"New tunnels must be approved by Hamas, and if you own your own tunnel, Hamas charges a fee," said one former senior intelligence officer, who is still working covertly in Rafah. Goods that make the trip of about 500 yards are subject to a 30 percent tax.

Tunnel entrances are located inside homes on both sides of the border. Some use simple pulley systems to transport goods, and some are more sophisticated, with electrical tracks and lighting, said the intelligence officer.

He estimated that 60 to 70 tunnels are operating along the 7.5 mile-long border and said Israel and Egypt are aware of their locations.

Israel has presented Egypt with surveillance footage showing Egyptian border-security officers assisting the smugglers. The footage was also sent to Washington, reportedly in an attempt to encourage Congress to withhold aid to Egypt.

But Egyptian officials say Israeli claims that tons of weaponry have entered Gaza through the tunnels are greatly exaggerated.

"Less than 10 percent of what Israel claims has been smuggled. The numbers they mention are technically impossible," said an Egyptian official in Israel. "American teams have visited the area."

Egypt also points out that Israel has rejected its requests to increase the number of officers on the Rafah border, a number limited under the 1978 Camp David Accords.

The current allotment of 750 officers is not enough, said the Egyptian official. "One-third are at rest, one-third are training, and one-third are on duty" at any given time, he said.

Egypt has also used U.S. funds to purchase a multimillion-dollar ground sensory system to detect the tunnels. U.S. teams will train the Egyptians to use the system, which can pick up sounds and movements underground.