Gunboats of the Serb-dominated federal military Wednesday blocked a convoy carrying Yugoslavia's Croatian president, other leaders of breakaway Croatia and about 500 displaced Dubrovnik residents from reaching the famed Adriatic town, the Tanjug news agency reported.

Tanjug, quoting reports on the radio station in the central Adriatic port of Split, said the flotilla of about 100 private boats and yachts led by the ferry Slavija I was halted by gunboats off the island of Mljet at 6:30 a.m.Naval commanders demanded the Slavija I, carrying Yugoslav President Stjepan Mesic and other leading politicians and members of the intelligencia of independence-minded Croatia, divert to the port of Zelenika, about 40 miles southeast of Dubrovnik.

Tanjug said the commanders ordered the rest of the flotilla to turn around.

Mesic, reportedly in radio contact with Adm. Stane Brovet, the deputy Yugoslav defense minister in Belgrade, rejected the directives, it said.

Negotiations were continuing between Mesic and Brovet, Tanjug said.

The convoy departed Tuesday evening from Split, carrying to Dubrovnik about 500 people who fled the city and when troops of the Serb-dominated Yugoslav army besieged the region Oct. 1.