* Speech by Fed Chair Yellen next in focus

* Dollar up against euro, lower against yen and franc

* Long-term dollar uptrend remains (Updates prices, adds comments; changes byline, dateline, previous LONDON)

By Sam Forgione

NEW YORK, March 27 (Reuters) – The dollar posted minor gains against the euro on Friday while slipping slightly against the yen and the Swiss franc as bullish bets on the dollar lost some steam ahead of comments from Federal Reserve Chair Janet Yellen.

Yellen will speak on monetary policy in San Francisco at 3:45 p.m. EST (1945 GMT) and traders will keep an ear out for clues on when the Fed may begin tightening monetary policy.

Traders were wary of bidding up the dollar ahead of the speech after the currency posted its biggest one-day rise against a basket of major currencies in a week on Thursday. The euro was last down 0.08 percent at $ 1.0876 after rising above $ 1.10 over the prior three sessions.

“Until there is a bigger news event, it seems like the (euro’s) downside is demarcated near the lows in $ 1.08 and the top side is $ 1.1050,” said Alan Ruskin, global head of currency strategy at Deutsche Bank in New York. “Yellen will be the arbiter in terms of which side of that range we’re going to go to.”

The dollar index, which measures the greenback against a basket of six major currencies, rallied over 25 percent from early May last year through March 17. The dollar has since given back a portion of those gains since after the Fed’s latest policy statement on March 18 suggested a less aggressive timeline for hiking benchmark U.S. interest rates.

Analysts said the long-term uptrend in the dollar remained in place, however, given the likelihood that the Fed will hike rates this year and the recent start of the European Central Bank’s bond-buying stimulus in Europe.

“Nobody really wants to go home long euro, it’s not the good side of the market,” said Lane Newman, director of foreign exchange at ING Capital Markets in New York.

The dollar was last down 0.08 percent at 119.095 yen . The dollar was last down 0.1 percent against the Swiss franc at 0.96200 franc.

The dollar index was last down 0.1 percent at 97.338.

(Reporting by Sam Forgione; Additional reporting by Jemima Kelly in London; Editing by James Dalgleish)