PARIS--French economic growth will pick up slightly in the first half of 2015, as collapsing oil prices and a weaker euro amplify the impact of President François Hollande's tax cuts, national statistics agency Insee said Thursday.

In its first forecasts for the first six months of next year, the statistics agency said gross domestic product growth will rise to 0.3% quarter-on-quarter in the first two quarters of 2015, from 0.1% in the final three months of 2014.

"The pace of growth will be a little higher, compared with what we have seen since the spring of 2011," said Vladimir Passeron, an economist at Insee.

The more positive outlook for the French economy comes after a long period of near economic stagnation that has driven unemployment higher and derailed Mr. Hollande's plans to repair the country's finances.

Until now, even the French government has been cautious about the strength of the economic recovery next year, forecasting only a 1% expansion for the whole year. But based on Insee's forecasts for the first half of 2015, the economy would meet the government's target for the year, even if there were no further acceleration of growth in the second half.

That outlook will give Mr. Hollande cause for optimism half way through his five-year term in office. So far, poor economic results have made the Socialist leader the least popular president on record, according to opinion polls, and contributed to stinging defeats for his party in local and European elections.

The recent tumble in the oil price is already raising consumer spending power and improving the finances of companies, Insee said in its December economic outlook, entitled "the breaks are easing off a little." The weakening of the euro against the dollar since the summer is also a key reason for a brighter outlook, as it will help exporters sell their products on global markets, Insee said.

In its assessment of the impact on the French economy, Insee said the euro fell to $1.23 in early December from $1.37 on average in the second quarter, and oil fell to $78.4 a barrel in November from an average of $109.8 in the second quarter. Together the declines add 0.1 percentage point to quarter-on-quarter growth, and the economy could expand even faster if oil remains below $70 a barrel, or the euro falls further below $1.23, Insee said.

The boost to competitiveness and company finances from a lower euro and a lower oil price will coincide with an increase in tax cuts for employers. That will improve corporate margins and encourage investment and recruitment, the statistics agency said.

Still, despite the improvement in economic growth, Mr. Hollande will still miss his key target: bringing down unemployment. As the active population rises faster than jobs are created, unemployment will reach 10.6% in the second quarter of 2015, the highest level since 1997, Insee said.

There is also significant uncertainty around the forecasts. Business leaders could further delay investment and the volatility of oil prices is hard to predict, Insee said.

"We must be prudent because the oil price could rise as quickly as it fell," Mr. Palleron said.

Write to William Horobin at William.Horobin@wsj.com

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