MUMBAI, Dec 13 Reuters The Reserve Bank of India39;s efforts to slow the rupee39;s decline have been relentless but its alreadystretched strategy is now challenged by weak economic growth, tepid foreign inflows and a buoyant dollar39;s threat to Asian currencies, especially the Chinese yuan.

The dollar index has rallied more than 3 since Donald Trump won the U.S. presidential election on Nov. 5. The rupee has declined just 0.8 in that time, making it the secondbest among major Asian currencies, largely due to the RBI39;s intervention.

This intervention has stretched across segments buying and selling dollars in the onshore spot and forward markets, taking positions in local currency futures and in the nondeliverable forward NDF market.

The amount of intervention has been quite substantial … We can say intervention is a little bit stretched but, at the same time, it is a call that the RBI must take, said B Prasanna, head of global markets at ICICI Bank.

The strain is showing.

For instance, in the NDF market, the RBI39;s goto strategy, the central bank39;s position has ballooned to levels that make it difficult to use as frequently.

Moreover, India39;s forex reserves are at a fivemonth low after the RBI sold 38 billion, per IDFC FIRST Bank39;s estimate, between October and the first week of December.

Investors are taking notice.

The RBI39;s forex policy and the rupee39;s future were key discussion points in a recent Asia investment tour, said Madhavi Arora,…