TAMPA, Fla. — Seizing the Republican National Convention spotlight, vice presidential candidate Paul Ryan promised Wednesday night that Mitt Romney “will not duck the tough issues” if he wins the White House this fall and their party will move forcefully to solve the nation’s economic woes.

“After four years of getting the runaround, America needs a turnaround, and the man for the job is Governor Mitt Romney,” the Wisconsin lawmaker said in remarks prepared for delivery to a convention dogged by Tropical Storm Isaac. The storm, though downgraded from a hurricane, was still inflicting misery on millions along the nearby northern Gulf Coast.

In a secondary role if only for a moment, Romney accused Democratic President Barack Obama of backing “reckless defense cuts” amounting to $1 trillion. “There are plenty of places to cut in a federal budget that now totals over $3 trillion. But defense is not one of them,” Romney said in remarks that referred elliptically to the terror attacks of Sept. 11, 2001.

Romney spoke to the American Legion in Indianapolis as his aides in Florida scripted an economy-and-veterans-themed program in their own convention hall and kept a wary eye on Isaac. The storm remained a threat to levees in the New Orleans area almost exactly seven years after the calamitous Hurricane Katrina.

Ryan’s vice presidential acceptance speech marked a prime-time national debut by a 42-year-old lawmaker lauded by fellow Republicans for his understanding of the complexities of the nation’s budget.

Romney tapped Ryan earlier this month as his running mate, a selection that cheered conservatives who have doubted the presidential candidate’s own commitment to their cause.

If Ryan’s selection was designed in part to appeal to conservatives, the convention was scripted to strengthen the ticket’s appeals among women, Hispanics and others who prefer Obama over the Republicans, as well as veterans who supported John McCain in 2008.

Appearing before delegates on his 76th birthday, the Arizona senator joked that he “had hopes of addressing you under different circumstances,” a reference to the dreams he once had of speaking as the incumbent in the White House.

Without mentioning Obama by name, McCain accused the president of failing to lead — on military spending and grave international issues as well. “Sadly, for the lonely voices of dissent in Syria and Iran and elsewhere who feel forgotten in their darkness ... our president is not being true to our values,” he said.

But another convention speaker, Sen. Rand Paul of Kentucky, pointedly disagreed with Romney on defense spending.

“Republicans must acknowledge that not every dollar spent on the military is necessary or well-spent, and Democrats must admit that domestic welfare and entitlements must be reformed,” he said.

In excerpts released in advance of his speech, Ryan said, “The present administration has made its choices. And Mitt Romney and I have made ours: Before the math and the momentum overwhelm us all, we are going to solve this nation’s economic problems.

“And I’m going to level with you: We don’t have much time.”

As chairman of the House Budget Committee, Ryan is the architect of a plan to curb long-term deficits by reducing taxes and making deep cuts in accounts ranging from farm programs to education. He also advocates saving billions from remaking Medicare and Medicaid, the government’s health care programs for seniors and the poor.

The Medicare changes, in particular, are potentially incendiary in an election campaign. Democrats say that Romney, with his selection of Ryan, has accepted political ownership of a plan that would turn the program from one in which seniors’ medical bills are automatically paid into one in which the government would give them checks to purchase coverage at costs that would require them to dip deeper into their pockets.

Romney delivers his own nationally televised acceptance speech Thursday night in the final act of his own convention. The political attention then shifts to the Democrats, who open their own convention on Tuesday to nominate Obama and Vice President Joseph Biden for a second term.

Deep into a two-week stretch of national gatherings, the race for the White House is in a sort of political black hole where the day-to-day polls matter little if at all as voters sort through their impressions.

Despite the hundreds of millions of dollars spent on television commercials by the candidates, their parties and supporting groups, the race has appeared unusually close since Romney clinched his nomination last spring.

Only eight or so battleground states appear to be competitive, although Republicans say they hope to expand the campaign after Labor Day, particularly in industrial states struggling to recover from the worst economic recession since the Great Depression.

Yet for all of the attack ads and inflammatory rhetoric, the two campaigns tiptoed carefully around the storm ravaging the Gulf Coast, vying to demonstrate concern for the victims without looking like they were seeking political gain.

Obama told an audience in Virginia he had spoken on the phone with governors and mayors of the affected states and cities while aboard Air Force One earlier in the day. Romney’s aides let it be known he might visit the region once the storm had passed.

Romney’s reference to $1 trillion in defense cuts was a 10-year figure that combined reductions already enacted by Congress and reductions scheduled to begin next January as a result of Congress’ failure to reach agreement on a broad plan to cut deficits.

He did not say so in his speech, but most Republicans, including Ryan, voted for the first installment as well as the second.

The reference to 9/11 was glancing in a speech that accused Obama of unwise defense cuts. Romney noted the economy is the top issue in the race, but he said, “Our debates can change suddenly, with a ringing phone in the dead of night ... or a plume of smoke on a clear blue morning.

“The first job of government is to keep the American people safe,” he said, pledging to do so.

Democrats spent part of their time working to tarnish the Republican brand. They pointed to an ABC News report that said Romney’s campaign had held a reception in Tampa Tuesday night aboard a yacht flying the flag of the Cayman Islands.

Romney has been criticized for having investments there by Democrats who say the effect is to reduce his taxes.

In an appearance before University of Virginia students, Obama said he understood Republicans didn’t have much nice to say about his tenure in office. He told his listeners the GOP hoped to disparage him so much that they would either vote for Romney or sit out the election.