* reuters://realtime/verb=Open/url=cpurl://apps.cp./Apps/cb-polls?s=GCR01+30+9&st=Menu+G+C poll data

BENGALURU, Sept 18 (Reuters) - The Swiss National Bank will follow the European Central Bank and raise its key interest rate by 25 basis points on September 21, according to economists polled by Reuters, who said it would then remain at 2.00% until at least September next year.

Five consecutive interest rate hikes from the SNB - a cumulative 250 basis points - have helped inflation fall to 1.6% from its peak of 3.5% last year and remain within the central bank's 0%-2% target for the past three months.

Despite having one of the lowest inflation rates among major economies, SNB Chairman Thomas Jordan said after hiking the key policy rate to 1.75% in June "underlying inflationary pressure has risen further" and signalled more tightening was likely to come.

All but seven of 37 economists in the Reuters Sept. 12-18 poll predicted the SNB would hike rates by a quarter point to 2.00% at its quarterly meeting on Thursday. The others said there would be no change.

But the economy stagnating in the last quarter and showing signs of losing further momentum would likely dissuade the central bank from hiking further, the poll showed.

A majority of economists predicted rates would remain at 2.00% after this month's move until at least the middle of next year.

"On balance, we think the SNB will look through the recent low inflation and hike rates by 25 bps one last time to 2.00%, given policymakers' previous hawkish commentary," said Adrian Prettejohn, Europe economist at Capital Economics.

"With wage growth constrained and the economy grinding to a halt, the risk inflation materially picks up again in the coming quarters appears low...This will encourage the SNB to stop hiking rates after September."

Swiss inflation was expected to average 2.3% this year before falling to 1.5% in 2024.

The expectation of a 25 basis point hike and an extended halt mirrors that of the ECB, which raised its policy rates by a quarter point and signalled the end of its most aggressive tightening cycle in history last week.

A hike this week could help the Swiss central bank to maintain its bias towards a stronger currency, especially against the euro as the European Union is its largest trading partner.

Since departing from its long-held campaign to rein in the safe-haven franc last year, the central bank has actively intervened in markets to prop up the currency and keep imported inflation in check.

The franc is up more than 3% against the euro this year and has been one of the best performing major currency so far in 2023.

But the central bank's forex reserves fell for the third consecutive month in August, limiting the SNB's room to continue supporting the currency.

"The SNB is unlikely to be as direct as the ECB in signalling they are done, in our view, given the sensitivity to the currency, so a tightening bias through either FX or rates is likely," noted James Nelligan, strategist at JP Morgan.

"The inflation forecasts and guidance around intervention will be key markers and likely more important than the hike itself." (For other stories from the Reuters global economic poll: )

(Reporting by Prerana Bhat; Polling by Sarupya Ganguly; Editing by Alex Richardson)