(Updates after cabinet approves decree)

By Giuseppe Fonte

ROME, June 30 (Reuters) - Italy's government said on Thursday it was lending state-owned firm GSE 4 billion euros ($4.17 billion) to buy gas to boost stockpiles, as the country scrambles to tackle a gas supply squeeze from Russia.

Rome aims to have its gas storage system filled to at least 90% of capacity by the end of this year, up from 58% at present.

The state energy management agency Gestore dei Servizi Energetici (GSE) - which is formally in charge of promoting renewables - will help boost gas stockpiles as surging energy prices complicate operators' efforts to help meet the year-end target set by the government.

A draft decree seen by Reuters did not spell out where GSE would buy the gas, saying it could act in coordination with state-controlled energy firms and gas transport group Snam .

The scheme, first reported by Reuters last week, is part of a broader decree approved by Mario Draghi's cabinet on Thursday, which includes measures worth around 3 billion euros to help families and firms cope with sky-high electricity, gas and petrol costs.

This decree extends to the end of the third-quarter measures aimed at cutting electricity and gas bills for enterprises and households. These include lowering tax rates on natural gas, and subsidising energy supplies for low-income families.

The new measures come on top of more than 30 billion euros budgeted since January to soften the negative impact of surging energy costs, which are weighing on the growth prospects of the euro zone's third-largest economy.

Draghi curtailed his attendance at a NATO summit in Madrid to chair the cabinet meeting amid growing tensions in his multi-party coalition, with parties already jockeying for position ahead of a national election early next year.

Italy last year got about 40% of its imported gas from Russia and, like other EU nations, has begun efforts to diversify its energy supply mix in the wake of Moscow's invasion of Ukraine.

($1 = 0.9591 euros) (Reporting by Giuseppe Fonte, editing by Angelo Amante and David Evans)