NEW YORK (Reuters) -U.S. companies are getting ready to open their books on the second quarter, with investors looking for signs of an impact from President Donald Trump's trade war launched on April 2.

While earnings growth is expected to decelerate from the first three months of the year, a sharp decline in the dollar could help to offset possible tariff effects.

Analysts are forecasting second-quarter growth of 5.8% year-over-year compared with 13.7% in the first quarter, LSEG data show. JPMorgan Chase and other big banks are due to report results on July 15, unofficially kicking off the reporting period.

The S&P 500 index has returned to all-time highs, raising questions again on whether profit growth will be enough to support stocks at higher prices.

The index is trading at a multiple of about 22 times forward earnings, compared with a 10-year average price-to-earnings ratio of roughly 18, based on LSEG data.

Trump broadened his global trade war on Tuesday, announcing plans to impose a 50% tariff on imported copper, and said long-threatened levies on semiconductors and pharmaceuticals were coming soon.

On Monday, Trump told 14 nations including Japan and South Korea that they now face sharply higher tariffs from a new deadline of August 1.

Countries have been under pressure to conclude deals with the U.S. since Trump unleashed the trade war, causing a sharp selloff in stocks. Only two deals have been struck so far, with Britain and Vietnam. In June, Washington and Beijing agreed on a framework covering tariff rates.

With the first-quarter earnings season, "it was kind of like, we really don't know what to expect. There were a lot less companies pulling guidance than anticipated, and it showed companies were still relatively resilient," said Keith Lerner, chief market strategist at Truist Advisory Services in Atlanta. 

"The question was, maybe they're resilient because we haven't really seen the impact."

Tariffs are expected to increase prices and slow down growth, though uncertainty over the ultimate policies has also been a drag since it leads businesses to postpone decisions.

While trade negotiations are still under way, tariffs will likely again be a topic on many company conference calls, said Peter Tuz, president of Chase Investment Counsel in Charlottesville, Virginia.

Higher tariffs have yet to weigh on sales forecasts or corporate spending plans at the aggregate index level, David Kostin, Goldman Sachs' chief U.S. equity strategist and his team wrote.

However, they cited risks to some corporate margins, if companies are forced to absorb tariff costs. Goldman Sachs economists expect consumers to absorb 70% of the direct cost.

Second-quarter earnings growth forecasts have stabilized in recent weeks after falling sharply in early April.

The initial negative earnings revisions followed Trump's "Liberation Day" tariff announcements in April, while expectations for tariff-exposed sectors such as autos, transportation and consumer durables remain steeply below April levels, Sean Simonds and other equity strategists at UBS wrote in a note.

Over the last three months, the estimated second-quarter earnings growth rate declined 4.4 percentage points, compared with the prior three-year average drop of 3.5 points, according to Tajinder Dhillon, senior research analyst at LSEG Data & Analytics.

Strategists say that is not necessarily a negative, since most S&P 500 companies typically beat analysts' earnings estimates and lower expectations can mean a lower bar to beat.

"Expectations are sufficiently low for many S&P 500 companies to show much better-than-expected Q2 earnings growth," Nicholas Colas, co-founder of DataTrek wrote in a recent note.

That the S&P 500 has recently hit a record high "says that the market sees things the same way," he wrote.

He and others see a possible benefit to earnings from the U.S. dollar's weakness, which makes U.S. goods less expensive overseas.

The dollar index, which measures the greenback against a basket of currencies, fell about 7% in the second quarter. It is down about 10% year to date and had the biggest drop over the first six months of any year since 1973.

"A lot of the big Fortune 500 companies do half their business overseas, so it might be a source of positive surprises for some companies, and maybe enough to offset what they might say about the tariffs going forward," Tuz said.

Technology shares rebounded sharply in the second quarter, rising 23.5% after falling in the first quarter. Communication services also rebounded in the second quarter.

The two sectors are expected to have had the biggest earnings growth from a year ago in the second quarter, with technology earnings seen up 17.7% from a year ago and communication services up 31.8%, based on LSEG data.

Optimism about artificial intelligence remains high. Last week, the market value of Nvidia, the leading designer of high-end AI chips, neared $4 trillion, briefly putting it on track to become the most valuable company in history.

"You need the big names, the megacaps to not disappoint in a big way," said Robert Pavlik, senior portfolio manager at Dakota Wealth in Fairfield, Connecticut.