(Adds New York to dateline, updates with New York closing copper
prices, adds analyst comment)

By Pratima Desai and Humeyra Pamuk

NEW YORK/LONDON, May 21 (Reuters) - Copper prices slipped on
Wednesday as stocks rose and the market fretted about rising
supplies, while aluminium rose on expectations China would become a
net importer in the second half of the year.

Battery material lead MBP3 fell to its lowest in nearly a year
on the London Metal Exchange, while nickel MNI3 slid to levels
seen last August.

London copper MCU3 for three-month delivery closed at $8,240 a
tonne from $8,320 a tonne at the close on Tuesday.

At the New York Mercantile Exchange's COMEX division, copper for
July delivery HGN8 ended down 3.65 cents at $3.74 a lb.

Rob Kurzatkowski, futures analyst with optionsXpress in Chicago,
believed the weaker price action in the red metal has been in
response to the market's failure to cross the $4.00 (a lb) mark and
firmly close above it earlier in the month.

"I think some of the speculative money is either on the
sidelines or has flowed into the hot markets like precious metals
and oil," he said.

The metal used extensively in power and construction hit a
record high of $8,880 a tonne in April on the LME and $4.2605 a lb
on COMEX earlier this month as the market fretted about miners'
strikes in Chile and Peru.

"Copper was supported by strikes ... Stocks are rising, there is
less tension about supplies," said Eugen Weinberg, commodities
analyst at Commerzbank.

Stocks of copper in LME warehouses of around 125,000 tonnes have
risen by more than 10 percent since early May.

"There is legitimate concern about more supply coming into the
market over the months ahead," MF Global said in a note.

Analysts said the market was also worried about demand from the
United States, where the housing market is in recession, and from
China which has ample stocks.

More available material is reflected in premium for cash
material over the three-month contracts -- the backwardation -- down
nearly $100 a tonne from almost $160 at the start of May.

NET IMPORTER

Energy-intensive aluminium ended at $3,020 from $2,997 on
Tuesday. The metal used in power, transport and packaging has been
boosted by concern about supplies from China, the world's biggest
consumer and producer.

The earthquake in China's Sichuan province last week has helped
support prices, but the region produces only between 500,000-700,000
tonnes of aluminium a year, a fraction of the total capacity at
about 12.5 million tonnes.

More pertinent is the rising cost of electricity, which accounts
for about one-third of production costs estimated at an average
around $2,400 a tonne, and the chances of some Chinese smelters
closing down.

"Costs in China are rising big time, coal prices have picked up
again. China will become a net importer in the second half of the
year ... Prices will go up," Weinberg said.

He said tin prices were also supported by production shortfalls
in Indonesia, the world's second biggest producer.

Tin MSN3 hit a record high $25,500 a tonne on May 9, a gain of
nearly 60 percent since the start of the year. It closed at $24,300
from Tuesday's last quote at $23,655/23,700.

Nickel fell to a session low $25,140 a tonne and closed at
$25,300 from $26,000.

Used for making stainless steel, nickel has come selling
pressure on news that many mine projects delayed or postponed over
the last couple of years would soon be producing.

Lead slipped to $2,129 a tonne, a loss of more than 40 percent
since the metal hit a record high last November. It ended at $2,147
from $2,170/2,175 on Tuesday.

Prices have fallen because of rising stocks, which at around
65,000 tonnes, are up more than 40 percent since February.

Zinc MZN3 closed at $2,205 a tonne from $2,275 on Tuesday.
Metal Prices at 1745 GMT
Metal Last Change Pct Move End 2007 Ytd Pct
LME Cu 8240.00 -80.00 -0.96 6670.00 23.54
SHFE Cu* 62330.00 -630.00 -1.00 56880.00 9.58
LME Alum 3020.00 23.00 +0.77 2403.00 25.68
SHFE Alu* 18950.00 -330.00 -1.71 18180.00 4.24
COMEX Cu** 375.35 -3.70 -0.98 303.05 23.86
LME Zinc 2200.00 -75.00 -3.30 2370.00 -7.17
SHFE Zinc* 18160.00 -375.00 -2.02 18950.00 -4.17
LME Nick 25100.00 -900.00 -3.46 26350.00 -4.74
LME Lead 2147.00 -83.00 -3.72 2550.00 -15.80
LME Tin 24100.00 -500.00 -2.03 16400.00 46.95
** 1st contract month for COMEX copper
* 3rd contact month for SHFE AL, CU and ZN SHFE ZN began trading on
26/3/07
(Additional reporting by Chris Kelly in New York; Editing by
Marguerita Choy)