CAIRO, April 15 (Reuters) - Egypt, facing the worst energy shortages for years, has set limits for electricity use at mosques as part of government efforts to ease the impact of power cuts already affecting homes and factories.

The religious endowments minister has ordered mosques not to run air conditioners before May 15 and after that date to use air conditioning only during prayer time and half an hour before and after the call to prayer.

Mohamed Mokhtar Gomaa said in comments reported by state newspaper Al-Ahram that he would also ensure that electricity meters were installed at mosques that do not have them.

Widespread blackouts are expected this summer when Egyptians crank up their air conditioning and increased demand stresses the aging power grid, forcing the government to take measures to cut energy use.

The trade, industry and investment ministry has banned the making or importing of air conditioners that can be set lower than 20 degrees Celsius (68 Fahrenheit).

Chaos in the energy sector, kept going by oil handouts from Gulf Arab countries, will be among the biggest challenges facing the country's next president, who will take office this summer after elections scheduled for late May.

Long lines at gas stations and power cuts fuelled popular anger against Islamist President Mohamed Mursi ahead of his ouster by the army last summer.

The government said on Saturday that it would not be able to prevent power cuts this summer. (Reporting by Maggie Fick and Stephen Kalin; Editing by Louise Ireland)