LIMA, Nov 7 (Reuters) - Peru's central bank surprised the market on Thursday by cutting the benchmark interest rate for the first time in more than four years in a bid to spur economic growth and ward off an extended slowdown.

The bank lowered the rate to 4 percent from 4.25 percent, saying the economy is growing more slowly than its potential growth rate and that preliminary data does not yet point to a turnaround.

"Current and advanced indicators of productive activity show weakening in economic activity, reflecting less growth of our exports that is linked to the slowdown in economic activity of our trade partners and lower export prices," the central bank said in a statement.

Peru, a top global exporter of copper, gold and silver, enjoys one of the region's fastest-growing economies.

But weaker mineral prices and softer demand from major buyers such as China have dampened growth more than expected this year, setting the stage for the first trade deficit in more than a decade.

In 2012 Peru clocked a 6.3 percent expansion. So far this year, the economy has grown by 4.9 percent.

Once-surging domestic demand that helped offset dips in exports in previous years has also mellowed.

Construction, which expanded by nearly 20 percent last year, has grown at a more moderate pace in recent months. In September, demand for cement - a key indicator for construction - shrunk 1.2 percent.

The central bank stressed that further rate cuts would not necessarily follow.

"This decision is preventive and does not imply a series of reductions to the benchmark interest rate," the bank said.

The central bank had held the rate at 4.25 percent since May 2011, and had not lowered it since August 2009 - in the middle of the global financial crisis.

All 18 foreign and local economists surveyed by Reuters this week had forecast that it would hold the rate steady once more.

Annual inflation - now 3.04 percent - will likely hover around the upper limit of the central bank's 1 percent to 3 percent target range in coming months and then converge toward a 2 percent goal next year, the central bank said.

Last month the bank said it might change what it considers Peru's potential growth rate - the maximum pace the economy can expand without stoking inflation - to around 6.2 percent from 6.4 percent.

The central bank has already revised its estimate for economic growth this year to 5.5 percent, down from an earlier estimate of 6.1 percent.