In light of the expected shortage of natural gas in coming months, the Environmental Protection Ministry has given the Israel Electric Corporation the green light to use fuels that emit greater pollution, even at power stations in the densely populated areas of Tel Aviv and Haifa.

One stipulation is that the fuels are only to be used after all other options for supplying electric power from other stations have been exhausted.

The IEC is expected to have to move to heavier polluting fuels in a few weeks. A few weeks ago the cabinet authorized use of the more polluting fuels at Tel Aviv's Reading Power Station. However, Tel Aviv residents have demanded that the decision be reversed due to health concerns.

To determine the level of exposure to pollution, the Environmental Protection Ministry has made predictions as to how the pollution particles will be dispersed according to the conditions in each area. For example, to answer the question of whether pollution will exceed allowable levels by using mazut and diesel fuel in Ashdod, Haifa and Tel Aviv, the ministry has estimated quantities of key pollutants that will be released - such as nitrogen and sulfur - as well as microparticles in air pollution.

According to the ministry's tests, the use of the more polluting fuels at Reading will increase air pollution only minimally in Tel Aviv. However, the need to clean the chimneys every few days when these fuels are used could cause significant pollution and soot. In the past, residents of north Tel Aviv complained of heavy soot damage to their cars, windows and laundry during such cleaning.

The ministry has determined that parts of the Ashdod power station will be the first to move to mazut and diesel if necessary. The decision is based on the assumption that the dispersal of pollutants from that station will not reach the center of the city, and because the station is relatively distant from residential areas. After Ashdod the stations at Ramat Hovav (near Be'er Sheva ), Tzafit (near Kiryat Gat ) and Gezer (central Israel ) will make the move, after which more parts of the Ashdod power station will use the lower-grade fuels. Haifa and Tel Aviv will be the last to operate on diesel and mazut. The ministry decided that Tel Aviv would come before Haifa, because Haifa has high pollution already and use of the lower-grade fuels could push its pollution over allowable limits.

The ministry also determined that Reading's chimneys would be cleaned only when conditions allow the soot to disperse away from residents' homes. However, a senior ministry official conceded: "Sometimes the wind conditions are not suitable and there is no choice but to clean the chimneys so the station can operate."