An unannounced boat trip to Cuba by seven exile activists intent on challenging a government edict against such forays was cut short Thursday when armed U.S. Coast Guard officers intercepted them south of Key West, seized their vessel and escorted them back to South Florida.

Members of the Miami-based Democracia Movement, known for organizing protest flotillas in the Straits of Florida, said they were testing government resolve on the 50th anniversary of the signing of the U.N. Universal Declaration of Human Rights, being marked around the world Thursday.

Democracia spokesman Norman Del Valle said organization leader Ramon Saul Sanchez and six others aboard the motorboat, dubbed the Human Rights, planned to disembark in Havana to join a dissident demonstration pegged to the anniversary.

By stopping them, Del Valle contended, the Clinton administration violated the declaration's guarantee that all persons may freely return to their country of origin. The Coast Guard seized another Democracia boat in Key West last year when Sanchez set out on a flotilla and refused to say he would not enter Cuban waters. The government later returned the boat to the group.

``They keep violating our rights, and we keep claiming our rights,'' Del Valle said. ``We hope the President realizes he is committing an injustice.''

The Coast Guard said it was simply following the letter of a presidential order that requires boats leaving most Florida ports bound for Cuban waters to obtain a permit beforehand.

Administration officials have defended the legality of the order, specifically tailored to curb trips into Cuban waters by Democracia, saying it is necessary to prevent confrontations with the Cuban regime and protect American lives.

Del Valle said Democracia leaders didn't bother to apply for a permit because they believe it would be automatically denied. Sanchez once applied for and was denied a permit.

``If you want, I will go down there tomorrow to apply for one and we'll see what answer we get,'' Del Valle said.

Echoing previous complaints by Sanchez, Del Valle charged the government with a double standard in enforcing the order, saying that other private vessels are allowed to travel from Florida to Cuba unmolested to participate in an annual regatta or dock at the famed Marina Hemingway.

Because the presidential order requires boat captains stopped by the Coast Guard to say whether they intend to travel to Cuba, he added, it also raises issues involving prior restraint and the Fifth Amendment, which protects against self-incrimination.

``The order is illegitimate. They have no constitutional right to ask that question,'' Del Valle said.

He insisted that Sanchez and his companions fully intended to land in Havana if allowed to proceed, carrying only copies of the human rights declaration.

``They were going with only the clothes on their backs, because they didn't know whether they would wind up in prison,'' he said.

He said the Democracia activists planned to leave surreptitiously aboard the Human Rights from Marathon in the Florida Keys, where the boat is docked. But Coast Guard officers boarded the boat, which the organization believes is under government surveillance, as the crew got ready to depart at around 2:30 a.m.

The officers permitted the boat to leave after Sanchez refused to say whether he was bound for Cuba, but a Coast Guard vessel intercepted the Human Rights about five hours later in international waters south of Key West and two armed officers came aboard, Del Valle said. For five more hours the boat moved at minimum speed while the officers awaited instructions from Washington.

At 12:40 p.m., the vessel was seized and turned back to Key West, Coast Guard spokesman Jeff Hall said. Sanchez and his fellow activists were not arrested and would be free to go upon arriving in the Keys, he said.