LONDON, July 3 (Reuters) - Copper prices firmed on Monday as hopes for economic stimulus in top consumer China were raised by slowing activity in the country's industrial sector while sliding inventories suggested a tighter market.

Benchmark copper on the London Metal Exchange (LME) was up 0.32% at $8,331 a metric ton at 0924 GMT. Prices of the metal used in the power and construction industries dropped to a four-week low of $8,141 last week.

Surveys of purchasing managers in China's manufacturing sector suggest that the world's second-largest economy lost momentum in the second quarter as demand weakened.

"Chinese industrial activity seems to be stalling. The market is hoping the government will do more in terms of stimulus," one metals trader said, adding that volumes would be subdued because of a U.S. holiday on Tuesday.

Supporting copper prices are inventories in LME-registered warehouses that have fallen 30% since June 6 to stand at 69,700 tons .

Cancelled warrants - metal earmarked for delivery - at 50% of the total suggest more copper is due to leave the LME system.

This and large holdings of copper warrants - title documents conferring ownership - have fuelled concern about availability in the LME system and created a premium for cash copper over the three-month contract .

On the technical front, resistance on the upside for copper comes in at about $8,375, $8,410 and $8,425, where the 50-day, 21-day and 200-day moving averages currently sit.

Elsewhere, large holdings of lead warrants and significant holdings of long futures positions have raised concerns about supplies on the LME market and created a premium for near-term contracts over those with long maturities.

The premium for the cash lead contract over the three-month contract was at $44 a tonne. Three-month lead fell 0.4% to $2,091 a tonne.

More generally, industrial metals have come under pressure from a stronger U.S. currency, which makes dollar-priced commodities more expensive for holders of other currencies.

Aluminium slipped 0.4% to $2,142 a metric ton, zinc retreated 0.9% to $2,366, tin was up 0.5% at $26,930 and nickel ceded 0.5% to $20,415.

(Reporting by Pratima Desai Editing by David Goodman)