(Adds analyst comment, updates prices, changes dateline)

By Eric Onstad

LONDON, March 19 (Reuters) - U.S. and London copper

prices scaled fresh multi-month peaks on Wednesday as

speculators extended buying on expectations that U.S. tariffs

will be slapped on the metal.

Benchmark three-month copper on the London Metal

Exchange (LME) was up 0.3% to $9,933 a metric ton by 1105 GMT,

its highest since October 8.

Most active May copper futures on the U.S. Comex exchange

climbed 0.6% to a 10-month high of $5.05 a pound.

U.S. President Donald Trump's 25% U.S. tariffs on steel and

aluminium products took effect last week and he has also ordered

an investigation into potential new tariffs on copper.

Systematic funds that use computer analysis were leading the

buying on the market largely based on surging momentum as

technical levels are broken, a trader said.

Some analysts warned, however, that the high prices were not

supported by supply/demand fundamentals.

"We've still got this pressure to get as much stuff as

possible across to America. The copper arb (arbitrage), which we

quote, that's continuing to blow out," said Dan Smith, head of

research at Amalgamated Metal Trading.

The premium on Comex copper over the LME price widened to a

record $1,193 a ton, surpassing a record peak hit on Tuesday.

"I'm actually quite nervous about what's going to happen in

three to six months' time because I think a lot of this is

rather artificial," Smith said.

Curbing gains was a stronger dollar index, which

makes commodities priced in the U.S. currency more expensive for

buyers using other currencies.

LME aluminium rose 0.7% to $2,672 a ton, nickel

climbed 1.9% to $16,555 and tin added 0.5% to

$35,415 while lead dipped 0.1% to $2,093.50 and zinc

lost 0.7% to $2,941.

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