HAVANA, JULY 21 -- Cuban police sealed off the Canadian and West German embassies in Havana today and tightened a security cordon around the Spanish Embassy after nine more Cubans slipped through during the night and broke in.

The latest arrivals brought to 18 the number of Cubans sheltered at the Spanish Embassy, exacerbating a bitter diplomatic quarrel between Madrid and Havana.

Extra police also were guarding the Italian ambassador's residence, where four young Cubans sought asylum Tuesday after climbing onto the roof.

Spanish Embassy officials expressed surprise that the latest nine had managed to elude a heavy Cuban police guard around their embassy.

"We don't really know how they got through," an embassy spokesman said.

The Cuban guard was reinforced Friday after five Cubans slipped in, three during a doorway scuffle between Spanish and Cuban police and asylum seekers.

An embassy spokesman said that of the nine newcomers, four climbed in from a nearby roof while five others broke into an upper window of the building in the early hours of the morning.

Later Saturday, police tightened security around the elegant embassy building overlooking the bay in central Old Havana, keeping passersby back and restricting traffic.

Spain, which recalled its ambassador Wednesday for consultations, is sending four or five extra members of an elite police unit to join four of their colleagues already protecting the inside of the embassy.

Cuba has said it will not allow any asylum-seekers at foreign embassies to leave the country and has demanded their surrender.

Regular police and some Interior Ministry security police surrounded the West German and Canadian embassies in Havana's Miramar district today. They blocked access roads, letting only official Cuban and embassy vehicles pass.

Diplomats at both these embassies said no Cubans had sought asylum there and that they had not asked for special protection from Cuban authorities.

Police officers questioned about the extra security said it had been ordered for next Thursday's Revolution Day Carnival. But diplomats said the main area of carnival festivities is in central Havana, a long way from the Canadian and West German embassies.

The police reinforcements were deployed following a special program screened by Cuban television on Thursday night accusing U.S., West German, Canadian and Czechoslovak diplomats of plotting to discredit Cuba through asylum bids by Cubans.

The allegations were denied by the U.S., West German and Canadian governments.

Wooden crowd barriers were also erected around the U.S. Interests Section in Havana. Western diplomats said this move could herald a future protest demonstration outside the U.S. mission.

The asylum quarrel with Spain followed a similar dispute between Cuba and its former communist ally Czechoslovakia over 14 Cubans who sought refugee at the Czechoslovak Embassy between July 9 and 16.

The Czechoslovak Embassy refugees all eventually surrendered but only after fighting among themselves, destroying embassy property and holding Czechoslovak diplomats hostage for several hours.

Czechoslovak diplomats said they suspected not all of the Cubans who sought asylum had been genuine refugees.

Three of the 14 Cubans who had sought refuge at the Czechoslovak Embassy accused Czechoslovak diplomats Thursday of encouraging them to seek asylum as part of a plot involving U.S. and West German diplomats.