WASHINGTON — The federal budget deficit has surged to $779 billion in fiscal 2018, its highest level in six years as President Donald Trump’s tax cuts caused the government to borrow more heavily in order to cover its spending.

The Treasury Department said Monday that the deficit climbed $113 billion from fiscal 2017. Debt will likely worsen, with the Trump administration expecting the deficit to top $1 trillion in 2019, nearly matching the $1.1 trillion imbalance from 2012.

The deficit worsened because tax revenue is not keeping pace with government spending. The government’s fiscal year runs from October to September, unlike calendar years that begin in January. Tax revenue was essentially flat in fiscal 2018, while spending increased 3.2 percent as Congress gave more funds to military and domestic programs.

Revenue generally tumbled after December when Trump signed into law $1.5 trillion in tax cuts over the next decade. The tax cuts have caused economic growth to accelerate this year with Federal Reserve officials anticipating gains of 3.1 percent. But the Trump administration initially promised that the tax cuts would pay for themselves through stronger growth — and there is no sign so far of that happening.

“The budget numbers make very clear that the faster growth isn’t stopping the deficit from increasing,” said Marc Goldwein, senior policy director for the Committee for a Responsible Federal Budget, a group that advocates for lower deficits.

Treasury Secretary Steve Mnuchin suggested in a statement that the underlying source of the widening deficit was growth in government spending, rather than the tax cuts.

“Going forward, the President’s economic policies that have stimulated strong economic growth, combined with proposals to cut wasteful spending, will lead America toward a sustainable financial path,” Mnuchin said.

But William Gale, a senior fellow at the Brookings Institution, noted that the tax cuts are unlikely to generate a long-term bump in economic growth. More important, most estimates suggest that the deficit will worsen as spending on Social Security, Medicare and other programs increase with the aging baby boomer population.

Gale said it’s generally better to reduce the deficit when the economy has improved, which can minimize the sting of any changes to spending and prevent steeper cuts to spending in the future.

The cost of financing the deficit has increased following Trump’s tax cuts, with the interest charged on the 10-year U.S. Treasury note rising to roughly 3.15 percent from 2.46 percent at the start of the calendar year.