Abductors seized the 19-year old son of President Spiro Kyprianou last night and today threatened to send the youth's head to his father unless a band of rightist prisoners was given amnesty.

The kidnapers set a deadline of 10 p.m. (3 p.m.) today for compliance with their demands, but the hour passed without any word on the fate of the youth, Achilled Kyprianou.

Political kidnapings here hae seldom resulted in either concession by the government on violence on the part of the kidnapers.

Political kidnapings here have sel-

The prisoners whose release is being sought belong to EOKA-B, the rightist underground movement that seeks to unite this Mediterranean island with Greece. EOKA-B was implicated in the 1974 attempt to overthrow the late President Markaios, a move which brought on the Turkish invasion and susequent do facto partition of the island. About two-thirds of the population here are of Greek descent and one-third of Turkish origin.

Tollowing news of the kidnaping, the Cabinet met for several hours. As the session broke up, President Kyprianou, who suffers from angina, had to be assisted from the room.

Achilles Kyprianous, the President's eldest son, was abducted last nights near a military service as a lieutenant in the National Guard, a 20,000-man, Greek-Cypriot force officered by mainland Greeks.

His mother apeared several times on television, making tearful pleas to the kidnapers for the release of her son.

The government had delayed disclosure of the abduction until today when, officials here said, a tape recending was received of the kidnaped youth's voice.

There were several theories here about the motive behind the kidnaping. Many Greek-Cypriots believed that it was carried out by family or friends of an individual prisoner who sought to obtain his release under cover of a general amnesty.

Nevertheless, the abduction occurred against the background of mounting leftist influence in the Kyprianou government, and this trend might have motivated the EOKA-B leadership to attempt a desperate bid to protect their men in prison. About a score of them are being held.

Nicos Sampson, the most notorious EOKA-B prisoner, issued a statement repudiating any prisoner release obtained by violence. Sampson was recently denied permission to leave Cyprus on parole for medical treatment abroad.

Other EOKA-B prisoners include the alleged head of the organization, gunmen convicted this year for involvement in the assassination of American ambassador Rodger Davies in 1974, and others implicated in the murder of leftists and recent bombings at the British base here. The bombings were triggered by the government's request for the extradition of an EOKA-B gunman currently living in England.

The EOKA-B movement was a successor to the EOKA movement against British rule over Cyprus. The Greek junta revived it in the 1970s in an effort to overthrow Makarios.

EOKA-B supporters have been the target of a slow but presistent purge in the army and the civil service. The campaign is sponsored by the Communist and Socialist parties which comprise the bulk of President Kypriano's support.

The kidnapers are demanding an end to further prosecutions of EOKA-B members.

Their operation seems more likely to result in an intensification of the compaign to root out EOKA-B officials and perhaps even calls for a final round-up of all EOKA-B members, estimated to number several hundred.

The key factor in the rightists' strength has been the National Guard and its Greek officers. Although men of young Kyprianou's unit have been detained for questioning, these days the Guard is believed ot be loyal to the government. Even the Retired Officers Association has denounced the kidnapping.