Havana ? For more than two decades, Jimmy Carter has worked to improve U.S. relations with communist Cuba. The former American president will give it another shot when he arrives today at the invitation of Fidel Castro.

During his 1977-81 presidency, Carter helped re-establish diplomatic missions in both countries, negotiated the release of thousands of political prisoners and made it possible for Cuban exiles to visit their relatives on the island and, for a short time, other Americans to travel here freely.

But a U.S. trade embargo is still in place after four decades, and relations are as chilly as they’ve ever been. So the 77-year-old Carter seems determined to try to plant the seeds for future dialogue when he meets with Castro, 75.

Carter will be the first U.S. president in or out of office to visit Cuba since the 1959 revolution that put Castro in power. Calvin Coolidge was the last American head of state to visit, in 1928.

During his trip, Carter “will have the opportunity to contact and meet with as many citizens as he wants to,” the Cuban Communist Party’s newspaper said.

Wayne Smith, who was the chief U.S. diplomat to Havana during the Carter administration, said he didn’t expect “any miracles.” But, he added, “Carter cannot achieve less than (President) Bush has, which has been zero.”

The Bush administration has hardened the U.S. stance toward Havana, promising not to ease trade sanctions until Cuba holds free elections and releases political prisoners.

Carter has emphasized this is a private visit, and he will not be negotiating with the Cuban government.

Nevertheless, the White House and Cuban exiles want Carter to talk bluntly with Castro about human rights and democracy.