WASHINGTON — For decades, the aging tourist mecca of Havana beckoned, but the United States did not make it easy for Americans hoping to visit. They had to justify their trips to a government agency, apply for licenses, sign up with a company organizing “people to people” exchanges, or circumvent the law altogether by flying somewhere else first.

As of Friday, the door will open a lot wider. While ordinary tourism remains banned by law, new rules put in place by President Obama will make it easier for Americans to visit Cuba than it has been for most of the last half-century. If airlines begin regular service between the United States and Cuba, as they quickly moved to do, it could soon be as simple as logging on to a computer to order a ticket and checking a box to say the trip serves a legitimate purpose.

The rules will usher in a new era of contact between neighbors that have been estranged for longer than most of their citizens have been alive. It will be easier not only to travel, but also to send money. American telecommunications providers, financial institutions and agricultural companies will be given more opportunities to do business in Cuba. Visitors will be allowed to spend more, use credit cards and even bring home up to $100 in Cuban cigars.

United Airlines announced on Thursday that it planned to seek approval to begin regular service to Cuba from Newark and Houston. American Airlines, which operates charter flights to Cuba from Miami and Tampa, Fla., said it was reviewing the rule changes.