CATCo Share News (CAT)

* Possible exemption for Mexico, Canada on tariffs easesinvestorfears

* Russell outperforms as U.S. domestic stocks in favor

* Industrials help drag down Dow; tech boosted by Autodesk

* Dow down 0.33 pct, S&P down 0.05 pct, Nasdaq up 0.33 pct(Updates to close, adds commentary)

By Sinéad Carew

NEW YORK, March 7 (Reuters) - The S&P 500 ended slightlylower after Wednesday's volatile session as investors struggledto get a read on U.S. trade policy after President Donald Trumppromised hefty import tariffs but then said Mexico and Canadacould be exempt.

After falling as much as 0.97 percent, the S&P regainedground after the White House appeared to add exceptions to itsstated plan to slap import tariffs of 25 percent on steel and 10percent on aluminum.

Worries about a potential trade war had intensified afterfree trade supporter Gary Cohn resigned from his position asTrump's top economic advisor late Tuesday.

But late on Wednesday White House spokeswoman Sarah Sanderssaid Trump is expected to sign something by the end of the weekwith "potential carve-outs for Mexico and Canada based onnational security, and possibly other countries as well"

"It makes investors less worried if the tariff isn't appliedso broadly. But it's speculation at this point. We have nothingin writing. If there's one thing we've learned from thisadministration it's that it could change by the time it's inwriting," Janna Sampson, co-chief investment officer at OakBrookInvestments LLC in Lisle, Illinois.

The Dow Jones Industrial Average fell 82.76 points,or 0.33 percent, to end at 24,801.36, the S&P 500 lost1.32 points, or 0.05 percent, to 2,726.8 and the NasdaqComposite added 24.64 points, or 0.33 percent, to7,396.65.

The Dow was dragged down partly by manufacturer stocks suchas Caterpillar, which fell 1.5 percent, and Boeing, which ended 0.5 percent lower.

Both those stocks have been under pressure since the tariffplan was first announced on Thursday as they could be hurt byboth higher metal prices and any retaliatory trade barrierserected by foreign countries where they sell their products.

The S&P energy sector was one of the weakest of theS&P's 11 sectors with a 0.8 percent drop as it was also weigheddown by a 2 percent drop in oil prices from data showinga rise in U.S. inventories and output.

The Russell 2000 index, which tracks U.S. small-capstocks, outperformed the larger-cap indexes with a 0.8 percentgain. Its more domestically focused companies are seen as havingless exposure if foreign governments retaliate by slappingtariffs on U.S. exports.

The S&P's technology index was also a bright spotwith a 0.6 percent increase. Its biggest boosts came from a 2.2percent increase in Facebook and a 14.9 percent jump inshares of software supplier Autodesk after itsquarterly report.

Advancing issues outnumbered declining ones on the NYSE by a1.09-to-1 ratio; on Nasdaq, a 1.68-to-1 ratio favored advancers.

The S&P 500 posted 14 new 52-week highs and three new lows;the Nasdaq Composite recorded 147 new highs and 19 new lows.

Volume on U.S. exchanges was roughly 6.74 billion shares,compared to the 7.79 billion average for the last 20 sessions.(Additional reporting by Sruthi Shankar in Bengaluru; Editingby Nick Zieminski and James Dalgleish)