SPRINGFIELD, Mo.  Senator John McCain said Wednesday that he wanted 45 new nuclear reactors to be built in the United States by 2030, a goal that he called “as difficult as it is necessary.”

In his third straight day of campaign speechmaking about energy and $4-a-gallon gasoline, the presumptive Republican nominee told the crowd at a town hall-style meeting at Missouri State University that he saw nuclear power as a clean, safe alternative to conventional sources of energy that emit greenhouse gases. He said his ultimate goal was 100 new nuclear plants.

Mr. McCain has long promoted nuclear reactors, but Wednesday was the first time that he specified the number of plants he envisioned. Currently, there are 104 reactors in the country supplying some 20 percent of the electricity consumed. No new nuclear power plant has been built in the United States since the 1970s.

“China, Russia and India are all planning to build more than a hundred new power plants among them in the coming decades,” Mr. McCain said in this pocket of Missouri that is reliably Republican. “Across Europe, there are 197 reactors in operation, and nations including France and Belgium derive more than half their electricity from nuclear power. And if all of these nations can find a way to carry out great goals in energy policy, then I assure you that the United States is more than equal to the challenge.”