In Washington, Mr. Gross is seen as the main impediment to an easing of the embargo, but there are also limits to what the president could do without Congressional action. The 1992 Cuban Democracy Act conditioned the waiving of sanctions on the introduction of democratic changes inside Cuba. The 1996 Helms-Burton Act also requires that the embargo remain until Cuba has a transitional or democratically elected government. Obama administration officials say they have not given up, and could move if the president decides to act on his own. Officials say that under the Treasury Department’s licensing and regulation-writing authority, there is room for significant modification. Following the legal logic of Mr. Obama’s changes in 2009, further expansions in travel are possible along with new allowances for investment or imports and exports, especially if narrowly applied to Cuban businesses.

Even these adjustments — which could also include travel for all Americans and looser rules for ships engaged in trade with Cuba, according to a legal analysis commissioned by the Cuba Study Group — would probably mean a fierce political fight. The handful of Cuban-Americans in Congress for whom the embargo is sacred oppose looser rules.

When asked about Cuban entrepreneurs who are seeking more American support, Representative Ileana Ros-Lehtinen, the Florida Republican who is chairwoman of the House Foreign Relations Committee, proposed an even tighter embargo.

“The sanctions on the regime must remain in place and, in fact, should be strengthened, and not be altered,” she wrote in an e-mail. “Responsible nations must not buy into the facade the dictatorship is trying to create by announcing ‘reforms’ while, in reality, it’s tightening its grip on its people.”

Many Cubans agree that their government cares more about control than economic growth. Business owners complain that inspectors pounce when they see signs of success and demand receipts to prove that supplies were not stolen from the government, a common practice here. One restaurant owner in Havana said he received a large fine for failing to produce a receipt for plastic wrap.

Cuban officials say the shortages fueling the black market are caused by the embargo. But mostly they prefer to discuss the policy in familiar terms. They take reporter after reporter to hospitals of frail infants, where American medical exports are allowed under a humanitarian exception. Few companies bother, however, largely because of a rule, unique to Cuba, requiring that the American companies do on-site monitoring to make sure products are not used for weapons.