WASHINGTON — Republicans are pouring government stimulus into a steadily strengthening economy, adding economic fuel at a moment when unemployment is at a 16-year low and wages are beginning to rise, a combination that is stoking fears of higher inflation and ballooning budget deficits.

The $1.5 trillion tax cut that President Trump signed into law late last year, combined with a looming agreement to increase federal spending by hundreds of billions of dollars, would deliver a larger short-term fiscal boost than President Barack Obama and Democrats packed into their $835 billion stimulus package in the Great Recession.

The administration is also expected to soon roll out its $1.5 trillion infrastructure package, which would include $200 billion in new federal spending, offset by unspecified cuts elsewhere.

The question is how much added fuel is good for the economy.

Fears that the extra economic boost could spark faster inflation and prompt the Federal Reserve to accelerate the pace of interest rate increases appear to be at least partially driving the stock sell-off that has rattled markets over the last several days. Higher interest rates would raise federal borrowing costs as the United States continues to borrow heavily — the national debt has topped $20 trillion and annual deficits are creeping up toward $1 trillion. Treasury officials said last week that the United States will need to borrow $441 billion in privately held debt this quarter, the largest sum since 2010, when the economy was emerging from the worst downturn since the Great Depression.