U.S. Federal Reserve Chairman Ben Bernanke today expressed concerns about the U.S. dollar saying the weak greenback has led to an “unwelcome” rise in U.S. inflation.

Bernanke also suggested that the Fed is unlikely to lower official interest rates further, though his remarks suggested that — barring a further rise in inflation expectations — the Fed probably won’t contemplate higher rates until there is more stabilization in home prices.

Still, Bernanke appeared to shift the policy debate away from economic and financial strains and toward inflation and the dollar, which could provide the basis for higher rates eventually.

“We are attentive to the implications of changes in the value of the dollar for inflation and inflation expectations and will continue to formulate policy to guard against risks to both parts of our dual mandate,” Bernanke said in prepared remarks delivered via satellite to an international monetary conference in Spain.

He said that, along with the Treasury Department, the Fed will “continue to carefully monitor developments in foreign exchange markets.” Fed policy, as well as the economy’s underlying strength, “will be key factors ensuring that the dollar remains a strong and stable currency,” he said.

Bernanke also signaled that downside risks to the economy remain even though the U.S. is likely to see “better economic conditions” in the second half of the year after a weak first half.

“Until the housing market, and particularly house prices, shows clearer signs of stabilization, growth risks will remain to the downside,” Bernanke said. And while consumer spending has been “a bit better than expected,” Bernanke said households still face “significant headwinds” from higher energy prices, a soft job market and tumbling confidence. Recent oil-price gains are also further risk to growth, he said.

National Bank Financial says that although Bernanke broached the question of the value of the U.S. dollar in today’s speech — a subject it usually avoids — that doesn’t mean a change in rates is imminent just yet.

In his remarks, NBF reports that it noticed a change in the Fed’s rhetoric. “Usually, the Fed says the currency is not of their responsibility. However, now that they see it as contributing to the unwelcome rise in import prices and the CPI, the Fed admits that it has become ‘attentive to the implications of changes in the value of the dollar for inflation and inflation expectations’,” it says.

NBF recalls that the Fed also showed concern about the weaker dollar contributing to the inflation problem back in 1978. And, at the time, its response was to raise interest rates. “Will history repeat itself?” NBF asks.

“At this point, we believe that is premature to talk about an increase in the Fed funds rate in 2008,” it concludes. “We see this morning’s comments more along the line of hawkish speeches from Fed officials that should be expected given the recent deterioration in inflation expectations. In our view, as long as domestic labour cost do not take off, the Fed’s barks will be worst than its bite – especially if GDP growth remains lacklustre as we expect in [the second half of 2008].”

“Nonetheless, today’s comments are a reminder that surging commodity prices have put the Fed in an uncomfortable position that could prod it to pull the trigger if economic growth proves to be more resilient than expected,” it adds.