* Trump to make announcement on tariffs later today
* Express Scripts jumps after Cigna's $53 bln bid
* Dow down 0.18 pct, S&P up 0.04 pct, Nasdaq up 0.23 pct (Updates to early afternoon)
By Sruthi Shankar
March 8 (Reuters) - U.S. stock indexes traded in a narrow range on Thursday as investors digested President Donald Trump's latest comments on his proposed hefty metal tariffs ahead of an announcement late afternoon.
Trump said he would initially stick with the 25 percent duties on steel imports and 10 percent on aluminum and that he had a right to drop out countries or add countries, creating uncertainty among market participants.
Trump, who is expected to proclaim the tariffs at 03:30 p.m ET, promised Canada and Mexico would likely be exempted from the tariffs if they agree on a trade deal with the United States.
"As has been in the past, what President Trump says and what finally actually materializes are two different things," said Randy Frederick, vice president of trading and derivatives for Charles Schwab in Austin, Texas.
"It might be just wise to sit on the sidelines before we get some more clarity."
At 12:41 p.m. ET, the Dow Jones Industrial Average was down 0.18 percent at 24,755.82.
The S&P 500 was up just 0.04 percent to 2,727.98 and the Nasdaq Composite rose 0.23 percent to 7,413.77.
Worries over the likelihood of a global trade war triggered by Trump's tariff plans have dominated markets since last Thursday, with Trump's chief economic adviser Gary Cohn's exit heightening such concerns.
The plan has faced with strong opposition from most of key partners, with Europe and China warning they would respond in the event of a trade war with the United States.
"If he (Trump) does announce much more draconian measures that are going to knock on to other products, I think there will be a sell-off," said Dec Mullarkey, managing director at Sun Life Investment Management based in Wellesley, Massachusetts.
Express Scripts was among the top boosts to the S&P 500, rising 9.4 percent after health insurer Cigna agreed to buy the pharmacy benefits manager for almost $53 billion. Cigna shares slipped 11.2 percent.
Kroger fell more than 10 percent after the supermarket chain issued a disappointing full-year profit forecast.
American Eagle Outfitters turned 8 percent lower after trading up premarket on concerns over falling margins.
Declining issues outnumbered advancers on the NYSE by 1,502 to 1,318. On the Nasdaq, 1,467 issues fell and 1,365 advanced.
Reporting by Sruthi Shankar in Bengaluru; Editing by Sriraj Kalluvila