President Obama this week defended the nation's use of nuclear power, but a Gallup poll released this week indicates public confidence in the energy source has dropped in the midst of Japan's nuclear crisis.

According to the Gallup / USA Today poll, seven in ten Americans say that the nuclear emergency in Japan has made them more concerned about the threat of a similar incident in the United States. Thirty-nine percent of those surveyed indicated they are "a lot more concerned."

With its electrical power cut off and its back-up generators crippled by last week's tsunami, Japan's Fukushima Daiichi nuclear power plant has lapsed into a full-blown state of emergency. And though U.S. officials have assured the public that there is little chance that harmful radiation levels will reach the Pacific coast, fears of exposure have sparked a run on Geiger counters and anti-radiation potassium iodide.

"It is entirely possible we are going to see significant releases of radiation into the environment," James Acton, an associate in the nuclear policy program at the Carnegie Endowment for International Peace, said on FOX News. "But the chances of a catastrophic release of radiation...are very low."

Of the U.S.'s own 104 nuclear plants, 23 have the same General Electric Mark I containment design as the Fukushima plant, according to the Nuclear Regulatory Commission's online database. On Monday, GE Hitachi Nuclear defended the design, calling it the "industry's workhorse" with a "proven track record of safety and reliability."

Even so, 47 percent of respondents to this week's Gallup poll said they do not favor the construction of nuclear power plants, compared to 44 percent who expressed approval.

That's a shift from a poll taken March 3-6, before the earthquake and subsequent tsunami - when 57 percent of Americans said they favored nuclear power, Gallup says. Sixty-four percent of Americans also now say that Japan's natural disasters have made them more concerned about a major earthquake or tsunami happening in the U.S.

The poll has a four to five percent margin of error.