A stable US economy was vital for the globe, Letta told Obama, only hours after the US Congress staved off a debt default by agreeing to extend the government's borrowing authority.
After talks in the Oval Office, Letta congratulated Obama for ending the latest political drama in Washington to capture the world's attention.
"His success is also our success," Letta told reporters.
"Yesterday's decision was very important for the stability in the markets and the world.
"We need to have low interest rates; yesterday, we had the lowest interest rates in Italy for two years," he added. "That was for us a very important achievement."
Obama, meanwhile, hailed Letta's work to stabilize the Italian economy.
The US leader also praised Letta for winning a vote of confidence in parliament earlier this month.
"It is clear that Italy is moving in the right direction in stabilizing its finances and embarking on reforms that will make it more competitive," Obama said.
He also said the two discussed the importance of European growth and, not for the first time, expressed concern at the high rate of youth unemployment in Europe.
"We have great interest in Europe," Obama said.
"When Europe is doing well, that means we are doing well also," he added, vowing to work to complete a proposed transatlantic trade agreement in the coming months.
The two leaders also discussed regional security issues, including Syria, the need to shore up security and the fragile institutions in Libya and Italy's support for NATO operations in Afghanistan.
Letta told reporters at a separate press conference at the Italian Embassy that the deal ending the shutdown was "important to us, important to Europe and of course, it is important to the US."
He expressed hope that the Obama administration would work in the coming months to find a long-term, final solution to its budget problems.
The two leaders also touched on plans to launch the world's largest trade deal, which he said would be of great benefit to Rome.
"Italy and the United States are both committed to having these negotiations have a favorable outcome," Letta said, in remarks translated from Italian into English.
"Italy, of the 28 countries in the [European] Union, is the one that will draw the most from the conclusion of these talks, as it will allow us to enter the market more easily."
The Italian leader said that when Rome assumes the EU presidency next year, he will press for an early conclusion to the talks on the Transatlantic Trade and Investment Partnership (TTIP).
Letta joked that he had been pleased to see Parmesan cheese served at their White House lunch, offering it as an example of one of Italy's great exports - until a reporter reminded him that it is one of the most counterfeited products in the US.