BY NANCY SAN MARTIN

The U.S. Coast Guard in Puerto Rico scoured thousands of miles of open sea Monday in a search for a boat packed with at least 78 Dominican illegal migrants that has been missing for at least nine days.

''This is potentially the largest-recorded tragedy in recent years,'' said Eric Willis, a Coast Guard spokesman in San Juan. ``The search is by no means canceled, but we don't want to put out any false hope.''

''The likelihood of finding this [boat] being upright and people being alive is very unlikely,'' Willis said. ``But there is a chance. The Coast Guard is evaluating and pursuing every available avenue.''

The reports of the missing boat, a fishing craft commonly known as a yola, came as a record number of Dominicans has been fleeing the country in the midst of an economic crisis that has sent unemployment rates soaring, caused the Dominican peso to tumble and forced the imposition of rolling power blackouts that last up to 24 hours.

Since Oct. 1, the start of the fiscal year, the Coast Guard has intercepted more than 5,500 Dominicans at sea, compared to 2,500 during the previous 12-month period. In addition, the U.S. Border Patrol has picked up more than 1,500 Dominicans who had made it to Puerto Rico, a U.S. territory.

Authorities say it is the largest flow of migrants since 1996, when the Coast Guard intercepted 6,273 Dominicans in the Mona Passage between the Dominican Republic and Puerto Rico, considered a highly dangerous stretch of sea because of strong and unpredictable currents.

According to various reports the Coast Guard has received from family members and witnesses, the yola left from Límon on the northern Dominican coast on July 30 with 72 people on board. The boat made a stop at another coastal town, Samaná, and picked up an extra six passengers before setting out for Puerto Rico.

On Thursday, the Coast Guard received a report from another group of migrants making the crossing that a yola fitting the description of the missing boat had been spotted north of Desecheo Island, off Puerto Rico's northwestern coast.

An extensive search by air and sea over a 4,500-square-mile area was conducted over the weekend with no success. But on Monday the Dominican navy found a group of 19 migrants on a string of uninhabited islands about 70 miles north of the port of Puerto Plata, on the Dominican Republic's north coast. That group left about four days after the missing boat, Dominican officials said.

Another yola that went missing in 2002 washed up in the same string of islands, known as the Silver Banks, after 12 days. The more than 70 migrants aboard survived.

''What this find has done is that it has validated some of our search criteria, and it's also validated that people are surviving in the sun this time of year,'' Willis said, adding that urgent messages were sent to cutters patrolling the region and an advisory was issued to mariners to be on the lookout.

The missing yola is believed to be a 35-foot open boat, probably powered by one or two outboard motors, and fast enough but not stable enough to cross the Mona Passage safely. Authorities said a boat that size should carry no more than a handful of passengers, but smugglers often pack such boats with dozens of illegal migrants.

No one knows how many Dominicans die crossing the Mona Passage. But the Coast Guard has documented at least 60 deaths since Oct. 1, compared to nine during the previous 12-month period.

''People are dying because they are getting in these grossly overloaded and very unseaworthy vessels in one of the most dangerous passages in the world,'' Willis said.