* Former FBI director to testify before Congress on Thursday
* UK election in focus
* Navistar dips after posting quarterly loss
* Indexes up: Dow 0.11 pct, S&P 0.10 pct, Nasdaq 0.26 pct (Updates to open)
By Tanya Agrawal
June 7 (Reuters) - U.S. stocks opened slightly higher on Wednesday but gains were limited as investors stayed on the sidelines ahead of Thursday's major political and economic events.
Britain's general election, the European Central Bank's policy meeting and former FBI Director James Comey's testimony before a Senate panel could all weigh on investor sentiment.
Comey's first public appearance since he was fired by U.S. President Donald Trump might shed more light on a probe by the FBI into alleged Russian meddling in last year's U.S. presidential election.
His testimony could dampen already flagging momentum for Trump's legislative agenda of rolling back healthcare reforms and overhauling the tax code.
The closely-fought election in Britain is also keenly watched, with one poll showing Prime Minister Theresa May increasing her parliamentary majority, while another suggesting a neck-and-neck race with the Labour Party.
"It's the calm before the storm. We have a quiet week in terms of economic data and there's a general global unease at the moment," said Scott Brown, chief economist at Raymond James in St. Petersburg, Florida.
"The impact of Comey's statement really depends on what he says, and anyway these hearings are long and dragged out. The UK elections could have an impact if there is a hung parliament and the various polls are adding a level of uncertainty."
The ECB will also hold its policy meeting on Thursday and is expected to reiterate its plan to extend the money-printing scheme at least until the end of the year.
Safe havens turned attractive, with gold steadying near seven-month highs and U.S. 10-year Treasury yields hovering near lows not seen since the November U.S. election.
At 9:34 a.m. ET (1334 GMT), the Dow Jones Industrial Average was up 23.42 points, or 0.11 percent, at 21,159.65, the S&P 500 was up 2.63 points, or 0.10 percent, at 2,431.96.
The Nasdaq Composite was up 16.53 points, or 0.26 percent, at 6,291.59.
Seven of the 11 major S&P 500 sectors were higher, with the technology index's 0.33 percent rise leading the gainers.
Apple's 0.7 percent rise provided the biggest boost to the S&P and the Nasdaq.
Shares of Navistar International were down 3.1 percent at $29.15 after the truck and engine maker posted a quarterly loss.
Exact Sciences was down 5.5 percent at $35.55 after the diagnostics test maker said it was looking to raise $250 million in a stock deal.
Keysight was up 3.4 percent at $41.77 after the electronic measurement equipment maker's forecast topped expectations.
Advancing issues outnumbered decliners on the NYSE by 1,336 to 1,035. On the Nasdaq, 1,284 issues rose and 784 fell.
The S&P 500 index showed 28 new 52-week highs and 11 new lows, while the Nasdaq recorded 82 new highs and 70 new lows. (Reporting by Tanya Agrawal in Bengaluru; Editing by Anil D'Silva)