EGYPT has long been considered a "bridge" between the East and West. Yet, two weeks into the Israeli campaign against Hamas in Gaza, Egypt is probably better known for its role as a tunnel, serving as the primary smuggling route for Hamas weapons into militant-controlled territory. As pressure mounts for a cease-fire, the disposition of these tunnels - and specifically, what actions Cairo is prepared to take to close them - seems likely to prove the difference between war and peace.

Given the circumstances, Cairo should be anxious to end the smuggling. Egypt has been at peace with Israel since 1979 and has strong ties with the more moderate Palestinian Authority led by President Mahmoud Abbas. Hamas, with its historic links to the anti-government Islamist Muslim Brotherhood in Egypt, represents a significant threat to Cairo.

For decades, Egypt fought the Muslim Brotherhood, eventually getting the upper hand; today, while the Brotherhood remains quite popular, it ostensibly abjures violence. For Cairo, the prospect of Hamas hooking up with the Egyptian Muslim Brotherhood raises serious concerns of ideological contagion. Also troubling is Hamas's close ties to Iran, Egypt's foremost regional rival and detractor.

Egypt's security concerns hit home in January 2008, when Hamas destroyed the fence between Gaza and Egypt, allowing an estimated 700,000 Palestinians to cross the border. By March it was reported that Egypt had accepted $23 million from Washington to help secure the border and detect tunnels.

In June, Egypt brokered a cease-fire agreement between Israel and Hamas. But during the six-month period of relative calm that ensued, Hamas capitalized, improving its military capabilities by smuggling in some 80 tons of weapons from Egypt, including longer-range Iranian-made rockets that brought 10 percent of the Israeli population within striking distance.

It's unclear exactly what Egypt was doing while Hamas was engaged in this smuggling. According to Egyptian sources, its capacity to counter Hamas's extensive tunnel network was hampered by the peace treaty with Israel, which limits the number of troops allowed to be deployed in the Sinai. Or perhaps Cairo tolerated a certain extent of smuggling to demonstrate sympathy for Palestinians and maintain a modicum of goodwill with Hamas.

Despite what appears to have been a relatively laissez-faire attitude toward the tunnels, since the onset of the Israeli military campaign Cairo has kept the Gaza frontier closed, against Hamas's expressed wishes.

Today, as calls for a cease-fire reach fever pitch, a clear convergence of interest has emerged among Egypt, Israel, and the Palestinian Authority. All parties would like to see Hamas weakened. While it may be overly ambitious to hope the Israeli operation will result in regime removal in Gaza, ending the pipeline of weapons to the militant group would be an important step toward clipping its wings.

Given the dynamics on the border, any meaningful step toward curbing tunnel smuggling is likely going to have to occur on Egyptian territory. This will require Israeli flexibility and a commitment on Cairo's part. Although Cairo would likely be hesitant to accept additional foreign troops on its soil - multinational force observers are already in the Sinai monitoring the Israel-Egypt peace agreement - some element of international forces may be required to interdict the tunnels and seal the cease-fire deal.

Cairo has a clear interest in stopping the smuggling. By closing the tunnels, Egypt stands to temporarily stall if not reverse the regional trend toward "resistance" being promoted by Tehran. For Cairo, which has seen relations with Washington deteriorate during the Bush administration, seriously dealing with the tunnels would also present an opportunity to get off on the right foot with the Obama administration.

Countering the smuggling tunnels is the key to an enduring cease-fire. Should Cairo take a tough stand on the tunnels, Iran and its allies will no doubt be critical. But if Egypt is determined to stop the bloodshed, it will have to work with Israel and the Palestinian Authority to find an effective strategy to stem the flow of weapons. On Gaza, Cairo is the lone bridge to a solution.