BRUSSELS (Reuters) - The European Union investment plan, its flagship project to relaunch the bloc's sluggish economy, may have produced no added value, because private investment made through the plan might have been made anyway, EU auditors said on Thursday.

A European Fund for Strategic Investments (EFSI) was set up last year in a bid to boost funding for riskier companies and projects, in particular for infrastructure, education and research, that are most affected by low levels of investment in the EU.

The EFSI intends to use 21 billion euros ($23.52 billion) of EU guarantees and cash to attract private investment of at least 315 billion euros by mid-2018. The Commission said in September it plans to double the funding target of the program and to extend it to 2022, after data showed the plan has generated more than 100 billion euros of investment, in line with targets.

But the European Court of Auditors, the body assessing the regularity and performance of EU spending, said the investment plan may have no added value, as it is not clear whether it is attracting funds that would have been invested in any case.

"There is a risk" that EFSI may have no added value, ECA President Klaus-Heiner Lehne told reporters.

In a report released on Thursday, EU auditors said the launch of EFSI has delayed and reduced spending in other EU programs which were meant to fund infrastructure and research projects, the very operational fields of EFSI.

The Commission, in a written reply included in the report said that EFSI "did not affect the overall objectives" of the EU program for infrastructure funding.

An official for the European Investment Bank, the EU's financial arm and the main player in EFSI, said around three out of four clients benefiting from EFSI are new counterparts to the EIB, a sign that "EFSI allows EIB to finance projects it would have not undertaken otherwise."

EU BUDGET SIGNED OFF

In its annual report, ECA also signed off the EU accounts for last year, saying that EU funds were broadly spent according to the rules.

The overall level of error for payments has declined to 3.8 percent last year from 4.4 percent of spending in 2014, the report found.

Lehne, a former center-right lawmaker who became head of the ECA this month, said that this decline is not sufficient. The ECA's target for errors is 2 percent.

He added that the decrease in the level of errors is also not relevant from a statistical standpoint and therefore may not even have occurred. The court audits EU accounts on the basis of samples.

Errors are caused by funds spent not in line with EU rules, but which do not represent fraud or waste, for which other EU bodies are in charge of inquiries, auditors said.

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(Reporting by Francesco Guarascio, editing by Larry King)