In the three years since Hamas took control of Gaza, Israeli officials have employed mathematical formulas to monitor foodstuffs and other basic goods entering the Strip to ensure that the amount of supplies entering was neither less nor more than the amount Israel permitted, according to documents released last week.

The documents - released Thursday in response to a Freedom of Information Act petition by the non-profit group Gisha - were drafted while Amos Gilad served as interim coordinator of government activities in the territories, heading the body that checked the goods.

The formulas used coefficients and a formulation for "breathing space," a term used by COGAT authorities to refer to the number of days remaining until a certain supply runs out in Gaza, to determine allowed quantities.

In September 2007, the Israeli government ordered a tightening of the blockade on Gaza, a closure first put in place in 1991. COGAT, in conjunction with other authorities, drafted "Rules for permitting the entry of goods" and "Regulation, supervision and evaluation of supply inventories in Gaza."

Both documents were classified as drafts, but in effect served as instructions for Israeli authorities and were considered valid until a government-implemented policy change following the May raid of a Gaza-bound flotilla that left nine people dead.

Officials from COGAT, a Defense Ministry unit that coordinates activity between the government, military, international groups and the Palestinian Authority, told Haaretz that it had actually been responsible for releasing the documents, given that in the wake of the government decision the directives for keeping the files classified were no longer in force.

A high-ranking COGAT officer told Haaretz that "Regulation, supervision and evaluation of supply of inventories in Gaza" is a method of quickly identifying a shortage of any basic item in Gaza, and that despite the mathematical equations contained in the document, he had never intentionally limited the amount of goods allowed to enter, but on the contrary, verified whether inventories of certain basic supplies in Gaza were full.

The COGAT spokesman said that the regulations were formulated "based on well-known basic foodstuffs, in consultation with the Israeli Health Ministry and in consideration of family consumption habits in Gaza, as published by the Palestinian Central Bureau of Statistics in 2006."

The document contained "warning lines," which were defined as "the days of [remaining] inventory beyond which the relevant official must pay attention to the deviation from reasonable norms and examine the correctness of the model."

There were two types of warning lines. The "upper warning line," which identified surpluses, was defined as an inventory exceeding 21 days for products with short shelf lives or 80 days for those with long shelf lives.

The "lower warning line," which identified shortages, was defined as an inventory of less than four days for products with short shelf lives and of less than 20 days for those with long shelf lives.

The senior COGAT official said the upper warning line was never actually used and the lower line was an important tool for identifying and averting impending shortages.

The "rules for permitting the import of goods" was drafted pursuant to a cabinet decision to restrict "the quantity and type of merchandise" entering Gaza. Its stated purpose was to define the "procedure, rules and method under which permission will be granted" for goods to enter Gaza.

These rules, the draft continued, were meant to allow in goods that would "supply the basic humanitarian needs of the Palestinian population." It then listed seven considerations to weigh when determining which goods should be permitted.

Security was one. The others were as follows:

* "The necessity of the product for meeting humanitarian needs (including its implications for public health in both the Strip and Israel )."

* "The product's image (whether it is considered a luxury )."

* "Legal obligations."

* "The impact of the product's use (whether it is used for preservation, reconstruction or development ), with an emphasis on the impact of its entry on the Hamas government's status."

* "The sensitivities of the international community."

* "The existence of alternatives."

These rules explain why, for example, imports of cloth and thread, which were considered "development" products, were barred, thereby destroying Gaza's textile industry.

The document states that many outside parties affected Israel's decisions: The Strip's needs will be determined not only by the relevant government agencies, it read, but by the Palestinian Authority, international agencies, the media and petitions to the courts by nongovernmental organizations, among others.

The third document that COGAT gave Gisha was the official list of products allowed into Gaza prior to May's botched raid on a Gaza-bound flotilla.

Following that raid, the list was significantly expanded. But the senior COGAT official said that even before then, the list of products actually allowed into Gaza was always longer than the written list.