Adds closing prices, market details

By David French

April 1 (Reuters) - The S&P 500 and the Nasdaq Composite both closed higher on Tuesday, after a topsy-turvy day on Wall Street dominated by investor angst ahead of the impending tariff announcements from the Trump administration.

Financial markets have been volatile in recent weeks as investors assessed the economic fallout of U.S. President Donald Trump's extensive tariff plans, which have sparked worries about a U.S. economic slowdown and higher inflation.

Some of the uncertainty that has gripped markets is expected to dissipate after Trump unveils his tariff plan on Wednesday during an event in the Rose Garden, currently scheduled for 4 p.m. EDT.

However, while clarity on the specific tariff measures will be welcomed by investors, the overall backdrop is set to remain highly uncertain, making it difficult for markets to agree on directionality.

"The fact of the matter is sentiment is washed out and positioning is still fairly light," said Garrett Melson, portfolio strategist at Natixis Investment Managers Solutions.

"I don't think we're going to get the type of clarity that investors and business leaders want," he added. "And at the end of the day, we spend a lot of time talking about tariffs, but the bigger story is we are dealing with an economy that is not firing on all cylinders."

For now, according to Melson, this means investors are "sitting on their hands, biding their time."

This attitude was reflected in the three Wall Street benchmarks on Tuesday, which swung between positive and negative territory throughout much of the day, before finishing the afternoon with some decent momentum.

The S&P 500 .SPX gained 21.22 points, or 0.38%, to 5,633.07 points, while the Nasdaq Composite .IXIC climbed 150.60 points, or 0.87%, to 17,449.89. The Dow Jones Industrial Average .DJI edged down 11.80 points, or 0.03%, to 41,989.96.

Gains on the Nasdaq and S&P 500 were fueled by rebounds in technology stocks, which have been among the most punished in the opening weeks of the year.

Big-tech advances were led by Tesla TSLA.O, which climbed 3.6% ahead of its first-quarter vehicle deliveries report on Wednesday. There were also gains for other Magnificent Seven stocks including Amazon.com AMZN.O, Microsoft MSFT.O and Meta Platforms META.O, which rose between 1% and 1.8%.

The S&P, however, was also weighed down by falls in healthcare and airlines.

Johnson & Johnson JNJ.N was the worst performer on the S&P 500, falling 7.6% and dragging the broader healthcare sector .SPXHC down 1.8% to the bottom of the 11 S&P sectors. A U.S. bankruptcy judge rejected the company's $10 billion proposal to end tens of thousands of lawsuits alleging that its baby powder and other talc products cause ovarian cancer.

Meanwhile, Delta Air Lines DAL.N, American Airlines AAL.O and Southwest Airlines LUV.N all dropped between 2.4% and 5.9%, as Jefferies analysts downgraded stocks amid concerns that economic uncertainty could disrupt both business and retail travel demand.

Among single stocks, there were big gains posted by some of the newest public companies.

Conservative news outlet Newsmax NMAX.N soared for the second straight day, jumping 208%, following a more than 700% surge in its NYSE debut on Monday.

CoreWeave CRWV.O, which has had a more rocky start since debuting as a public company on Friday, climbed 37.3% to trade back above the IPO price of the artificial-intelligence startup.

Volume on U.S. exchanges was 15.09 billion shares, compared with the 15.83 billion average for the full session over the last 20 trading days.

(Reporting by Sruthi Shankar and Pranav Kashyap in Bengaluru and David French in New YorkEditing by Krishna Chandra Eluri and Matthew Lewis)

((sruthi.shankar@thomsonreuters.com; within U.S. +1 646 223 8780; outside U.S. +91 80 6182 2787;))