LAS VEGAS — Four days after his announcement as Mitt Romney’s running mate, Representative Paul D. Ryan was not in Florida talking Medicare with elderly voters or in drought-ridden Iowa talking about a farm bill. He traveled to the Venetian hotel here for a meeting hosted by Sheldon Adelson, the billionaire casino mogul who has pledged to spend as much as $100 million this year to defeat President Obama.

Mr. Adelson has already contributed more money to defeat Mr. Obama than anyone: over $50 million has gone to the 2012 campaign, including $10 million to a “super PAC” backing Mr. Romney and $10 million to Crossroads GPS, which has run millions of dollars of advertisements against Mr. Obama.

In keeping with Mr. Adelson’s penchant for staying below the radar, aides refused to say who attended the meeting with Mr. Ryan, though the location (a private room at one of Mr. Adelson’s hotels) and leaks from the Romney camp left little doubt. And in keeping with laws that prohibit elected officials from explicitly asking donors for super PAC money, aides to Mr. Romney insisted before the event that the meeting was not a fund-raiser.

“It’s a finance event, not a fund-raiser,” an aide told reporters. Asked if people were paying to attend, he repeated, “It’s a finance event, not a fund-raiser.”

Monte Miller, a longtime Republican donor who planned to attend, described it as an opportunity for major contributors and influential Las Vegas Republicans to size up Mr. Ryan.

“I’ve watched Ryan for the last few years,” Mr. Miller said. “I think I know what he’s going to bring. But I haven’t been in the same room as him. I want to see his charisma and communication skills.”

The meeting, attended by several dozen guests, underlines that Mr. Ryan not only helps bring ideological ballast to the ticket but also is expected to have major appeal to donors.

The campaign said $3.5 million rolled in — from large and small donors alike — within 24 hours after Mr. Romney named him on Saturday, and Mr. Ryan’s schedule through the party convention later this month quickly filled with 10 fund-raising events, including in Denver, Cleveland, Philadelphia and Detroit.

At each stop this week during a tour of battleground states, Mr. Ryan will attend fund-raising dinners and breakfasts in addition to public rallies.

Mr. Romney’s relationship with Mr. Adelson, not always warm, has improved in recent months through private meetings between the two — and by Mr. Romney’s appearance at a fund-raiser in Jerusalem last month attended by Mr. Adelson, who holds hawkish views in support of Israel.

Mr. Ryan’s connections to Mr. Adelson are looser — the casino magnate does not appear to have donated to Mr. Ryan’s campaigns or his political action committee — and his opinions on Israel and the Middle East peace process are less well defined.

“It’s a safe bet Israel will come up,” said one Republican donor in Las Vegas who is a friend of Mr. Adelson.

But a closer connection with Mr. Adelson also holds risks for Mr. Ryan and the Republican ticket. Mr. Adelson’s casino empire, which has made him a billionaire, is the subject of a federal investigation into whether his company, Las Vegas Sands, bribed Chinese officials to help him expand into the mainland. Mr. Adelson’s company has denied any wrongdoing and has attributed the accusations to a disgruntled former executive.

At the fund-raiser Mr. Adelson attended in Jerusalem, Mr. Romney’s assertion that cultural differences explained economic disparities between Israelis and Palestinians was criticized as ethnically insensitive. Mr. Romney also declared Jerusalem to be the capital of Israel and promised to move the United States Embassy there.

The campaign seized on Mr. Ryan’s new role to motivate Democratic donors, arguing that Mr. Romney chose his running mate to persuade wavering conservatives to open their wallets.

“Here’s the calculation,” Jim Messina, Mr. Obama’s campaign manager, wrote in a fund-raising pitch this week. Mr. Ryan is on the ticket to “inspire ultraconservative ideologues and corporate interests,” he said, adding, “that means tens or even hundreds of millions more dollars for the Romney campaign and the array of outside groups supporting him.”

The money, he said, would pay for attack ads. “Those ads will have more impact on undecided voters than anything Paul Ryan himself does or says,” Mr. Messina wrote, making his own appeal for donations to take countermeasures.

Trip Gabriel reported from Las Vegas, and Nicholas Confessore from New York.