BY NANCY SAN MARTIN

In the five months since the Bush administration tightened sanctions on Cuba, life has become ''very complicated'' for Yuceika, a Cuban woman who once survived on the $100 sent monthly from Miami by the father of her 12-year-old son.

''Before, I would have to really restrict spending so that the $100 would last a complete month,'' said Yuceika, 35, a resident of the north-central city of Matanzas who can no longer receive the money. ``Now, every day is a gamble.''

Yuceika is not alone. Numerous Cubans, and the Cuban government, have been harshly affected by the Bush administration measures, intended to hasten a transition to democracy by keeping U.S. dollars out of the Cuban government's coffers.

''We are challenging the regime in a way that it has not been challenged at least in the last 25 years,'' said Dan Fisk, deputy assistant secretary of state for Western Hemisphere affairs. ``They're feeling the pinch.''

U.S. officials say the tighter sanctions have already denied the Cuban government $100 million in income since they were implemented June 30, and they expect the total impact for their first year to hit $375 million.

The measures are widely considered unlikely to dramatically challenge the stability of Cuba's four-decade old communist government. But there is little question that Cuba and Cubans are feeling the pinch:

• The once-busy Havana airport terminal reserved for U.S. flights has been shut down. The 20 to 25 jetliners a week that used to fly from Miami, New York and Los Angeles to Cuba are down to a handful of much smaller planes, travel agents in Miami say.

• The number of U.S. travelers to Cuba, most of them Cuban Americans visiting relatives, is expected to drop from 180,000 in 2003 to no more than 30,000 in the first year of the new measures.

• Prices at Cuban government stores that sell imported products have soared by as much as 50 percent.

• Tourism dollars that trickled down to Cubans like taxi drivers and private restaurant and room-to-rent owners have dwindled, according to island residents.

• Saying it was reacting to the Bush measures, the Cuban government has imposed a 10 percent fee on most dollar exchanges -- in essence taking $1 out of every $10 that Cubans receive from people abroad.

The toughened U.S. rules restrict family reunification visits by Cuban Americans to Cuba to once every three years, instead of once a year, and limit gift parcels and the $1,200 a year cash remittances to immediate relatives -- parents, siblings and children, but not cousins or others.

Remittances from the United States alone total at least $400 million in a typical year, according to U.S. government estimates, while the family reunification travel and gift parcels total another $1.1 billion.

That estimate includes items such as the costs of airplane tickets, airport fees for excess baggage, and per diem expenditures authorized for visitors. Under the new rules, the per diem dropped from $164 to $50.

HALVING THE INFLOW

Fisk said the goal was to reduce money going into Cuba by 50 percent.

''That still keeps a flow going to the island, to the Cuban people, but it reduces the regime's ability to exploit those revenue sources,'' he said. ``The idea is to go after the regime.''

But average Cubans are feeling the pinch.

One example: Yuceika is not married to the father of her son, making her ineligible to receive the $100 a month that she used to get. And while the son is entitled to the money, he is a minor and cannot withdraw the cash in Cuba.

''I guess we'll have to wait and see how we manage,'' Yuceika told The Herald in a telephone interview from her home in Matanzas.

And while buyers still jam the government's so-called ''dollar stores'' -- which provide the state with huge profit margins on the otherwise unavailable imported items -- it remains unclear how long that will continue.

''The stores are still filled with people buying stuff because there's nothing to buy anywhere else,'' said James Cason, chief of the U.S. diplomatic mission in Havana. ``What we don't know is: Are people going to buy more or buy less as things get tougher and tougher? Will the measures lead to more money for the regime or less? . . . Only time will tell.''

Cason said another part of the new Bush policy on Cuba that seems to be working is the use of U.S. military airplanes, equipped as flying broadcasting stations, to force the signals of Radio and TV Martí past Cuban jamming. The planes have made seven such flights this year.

''On the information side, we are seeing people looking for TV Martí and they're finding it in some areas,'' Cason said during a recent visit to Miami. ``People are eager to see it.''

And in Washington, enforcement of the Cuba sanctions also has increased, officials said.

Of the approximately 63,000 requests for licenses to travel to Cuba processed by the Treasury Department from Aug. 10 to Nov. 10, about 36,000 were denied and 26,000 approved. U.S. regulations permit travel by humanitarian and academic groups, journalists and others as well as Cuban Americans.

Most of the travel licenses denied were ''incomplete, have been filled out by someone seeking to travel too soon after their last visit, they have false information or are seeking a license to visit someone other than immediate families,'' said Treasury spokeswoman Molly Millerwise.

Previous figures were unavailable.

ENFORCEMENT

Hundreds of civil penalties also have been issued to violators of travel regulations, with fines totaling more than $1.5 million in the year that ended Sept. 30. And at least five cases have been referred to law enforcement for criminal investigations, Millerwise said.

For Yuceika's son, the tighter U.S. restrictions make no sense. He was 2 years old when his father fled on a raft in 1994. He came to know his father again during his visits twice a year, the last one in June.

Now, he may not see him again until June 2007.

''This whole thing has caused my son to shed a lot of tears,'' Yuceika said. 'Now, more than ever, he wants to be with his father. Every Saturday, when his father calls he asks, `When are you getting me out of here?' ''

The boy turns 13 on Dec. 7. His father won't make it to the celebration.

"All he can do is wait for his father to call and wish him a happy birthday.''