OTTAWA -- A says only half of the $14.4 billion earmarked for the first phase of the federal Liberal government's infrastructure plan has been set aside for projects.

In a new report, the parliamentary budget office says 10,052 projects across 32 departments, agencies and Crown corporations have been approved for funding since 2016, with a combined cost to federal coffers of $7.2 billion.

That still leaves $7.2 billion to be allotted for projects that the Liberals had hoped would be underway or done by now.

A spokesman for Infrastructure Minister Amarjeet Sohi said all funding in the Liberal plan remains committed to provinces, territories and cities.

Funding does not flow in any year is shifted to future years, so it remains available for the projects and programs, Brook Simpson said.

The Liberals unveiled the first phase of spending in their 2016 budget, when they predicted resultant economic growth of 0.9 per cent in fiscal year 2016-17 and 1.4 per cent in the following 12-month period, which ends Saturday.

The parliamentary budget office estimates spending to date has boosted the economy by 0.1 per cent in each fiscal year and added between 9,600 and 11,100 jobs over the last 12 months.

But the estimates came with a caveat: Almost half of the projects the PBO reviewed didn't have identifiable start dates, making it tough to determine the "actual timing and magnitude of their economic impact," the report says.

Parliamentary budget officer Jean-Denis Frechette's concerns about the pace of federal infrastructure spending has been a thorn in the Liberals' side for more than a year. His office has repeatedly raised questions about delays in the government's spending plans.

Federal coffers are set to dole out $186.7 billion in infrastructure money over the next 12 years, but the most recent federal budget indicated that about one-quarter of planned spending between 2016 and 2019 was being moved to future years.

Slower-than-planned infrastructure spending could have implications for the budgetary balance sheet by reducing planned deficits in one year at the expense of deeper spending in future years, the watchdog says.