(Reuters) -U.S. stock index futures were muted on Friday as investors were risk-averse after President Donald Trump's tax and spending bill won a crucial House vote the previous day, raising concerns about the country's deteriorating fiscal outlook.

The Republican-controlled U.S. House of Representatives passed the sweeping tax and spending bill on Thursday that would enact much of Trump's policy agenda. The bill now heads to the Senate, which Republicans control 53-47, for approval.

If it becomes a law, the bill will add about $3.8 trillion to the federal government's $36.2 trillion debt over the next decade, according to the nonpartisan Congressional Budget Office.

"A ballooning debt could crowd out private investment, which could thereby slow down economic growth, and more importantly, it could limit the government's ability to respond to crises with spending," Charalampos Pissouros, senior market analyst at XM said in a note.

Long-dated government bond yields eased on Friday, with those on the 10-year note off 3.8 basis points to 4.51%.

At 05:16 a.m. ET, Dow E-minis were down 23 points, or 0.05%, S&P 500 E-minis were up 0.5 points, or 0.01%, and Nasdaq 100 E-minis were down 4.5 points, or 0.02%.

Most megacap and growth stocks were higher in premarket trading, with Tesla outpacing the rest with a 1.5% gain.

Shares of nuclear power firms soared after a Reuters report said Trump would sign executive orders aimed at jumpstarting the nuclear energy industry as soon as Friday.

Vistra gained 4.1% and the Global X Uranium ETF climbed 9.3%.

Deckers Outdoor slumped 16.8% after the maker of UGG boots said it would not provide annual targets owing to tariff-led macroeconomic uncertainty and forecast first-quarter net sales below estimates.

All three main stock indexes were set for modest weekly losses as worries about mounting U.S. debt pushed Treasury yields higher. Moody's downgrade of the U.S. credit rating late last week had initially sparked concerns.

Still, the S&P 500 and the Nasdaq were set for their best monthly showing of the year. A pause in tariffs, a temporary U.S.-China trade truce and tame inflation data have pushed equities higher, although the S&P 500 is still about 5% off record highs.

A Bank of America Global Research report stated that U.S. equities saw their fifth weekly outflow in six in the week till Wednesday.

At least three Federal Reserve officials including Kansas City Fed President Jeffrey Schmid are slated to speak later in the day.

Traders currently see at least two 25-basis-point rate cuts by the end of the year, with the first one anticipated in September, according to data compiled by LSEG.

Trading activity is expected to thin on Friday, heading into a long weekend, as markets will be shut on Monday for the Memorial Day holiday.