The three-day trip, the first by a U.S. president in 88 years, was unthinkable until Obama and Cuban President Raul Castro agreed in December 2014 to end an estrangement that began when Cuba's revolution ousted a pro-American government in 1959.

Plainclothes police have blanketed the capital with security while public works crews have busily laid down asphalt in a city where drivers joke they must navigate "potholes with streets."

Welcome signs with images of Obama alongside Castro popped up in colonial Old Havana, where the president and his family will tour on Sunday afternoon shortly after landing.

Since rapprochement, the two sides have restored diplomatic ties, signed commercial deals on telecommunications and scheduled airline service, and expanded cooperation on law enforcement and environmental protection.

"Obama has been brave for agreeing to relations with Cuba," said school teacher Elena Gonzalez, 43.

Major differences remain, notably the 54-year-old economic embargo of Cuba. Obama has asked Congress to rescind it but has been blocked by the Republican leadership.

Instead, he has used executive authority to loosen trade and travel restrictions.

Cuba also complains about the continued occupation of the naval base at Guantanamo Bay, which Obama has said is not up for discussion, as well as U.S. support for dissidents and anti-communist radio and TV programs beamed into Cuba.

"There are many years of mistrust and we are not going to change our system, our values," said Ileana Valdes, 55, a nurse. "Although one must highlight that there are no longer invasions."

The Americans in turn criticize one-party rule and repression of political opponents, and aides said Obama would address the issue publicly and privately.

Police briefly detained more than 200 activists in the days before the visit, dissidents said.

Obama's critics at home accuse him of making too many concessions for too little in return from the Cuban government and of using his trip to take a premature "victory lap" to polish his foreign policy legacy.

MAKING CUBA ENGAGEMENT IRREVERSIBLE

But Obama's more practical goal is to do everything he can in his final 10 months in office to make his Cuba policy changes irreversible, even if a Republican wins the White House in November's election.

Though general U.S. tourism to the island is still officially banned under the embargo, a sign of changing times was the presence of groups of U.S. travelers marveling at the vintage American cars rumbling through the streets and shopping for Cuba's trademark cigars and rum.

Little progress on the main issues is expected when Obama and Castro meet on Monday or at a state dinner that evening.

Instead, the highlights are likely to be Obama's speech on live Cuban television on Tuesday, when he will also meet dissidents and attend a baseball game between the Cuban national team and the Tampa Bay Rays.

"Times change and it's great that we have relations with the United States, even though they still impose the embargo," said Barbaro Echevarria, 28, a medical student. "But we can't blame all our problems on the U.S. embargo."

Underlining Obama's political challenge at home, the office of U.S. Representative Ed Royce, Republican chairman of the House Foreign Affairs Committee, said the president's "long record of unilateral, one-sided concessions has only served to prop up the communist Castro regime."

NO MEETING WITH FIDEL

Obama is not scheduled to meet retired president Fidel Castro, 89, but officials reminded Cubans of their "historic leader" by publishing photos in the Juventud Rebelde newspaper of Castro seated in a wheelchair and meeting with Venezuelan President Nicolas Maduro.

Maduro had just visited Cuba to receive its highest state honor in a show of defiance by socialist allies that have stood together against the United States since Maduro's predecessor, the late Hugo Chavez, came to power in 1999.

The photos of Fidel and the medal for Maduro underlined the conflicting sentiments within the ruling Communist Party about receiving a U.S. president.

At the same time official media published a glowing biography of Obama and the government signed a hotel management deal with Starwood Hotels & Resorts Worldwide.

Starwood becomes the first U.S. hotel company to sign a deal with Cuba since the 1959 revolution, announcing a multimillion-dollar investment to manage and market two properties in Havana and signing a letter of intent to operate a third.