Cypriot President Spiros Kyprianou was riding a wave of popularity today, based on sympathy and respect for his handling of rightist kidnapers who released his son unharmed early this morning.

Kyprianou has little inherent crowd-pleasing popularity but his enhanced prestige appears to make him a clear front-runner in February elections for the first full term since President Makarios' death earlier this year.

The president's son Achilles, 19. a second lieutenant in the national guard, walked into a LImassol police station after a two-hour hike down the wintry mountains from the six-foot-square pit where he said he was held since his abduction Wednesday. He said he received only bread and water while being held.

President Kyprianou refused to bow to the EOKA-B kidnapers' demand that 25 jailed members of the extreme rightist underground be freed. He did promise that the kidnapers themselves would be allowed to leave Cyprus for asylum in Greece.

It is not know what other concessions, if any, were granted in a pre-dawn meeting between the president and two EOKA-B kidnapers, with the Greek ambassador acting as mediator. The EOKA-B seeks union of Cyprus with Greece.

Cypriot and Western analysts concur that Kyprianou's new popularity will make him less dependent on the bloc of leftists supporting his presidential election bid.

Edging close to an above-the-parties status, Kyprianou is expected to slow the government's leftist pushed purge of the EOKA-B activists from the civil service and police.

A pledge along those lines may have figured in the bargaining for the young Kyprianou's release, but EOKA-B's effectiveness now appears broken, making the purge look vindictive rather than essential to forestall fresh subversion.

The kidnaping provided an opportunity for many EOKA-B supporters to dissociate from the organization, which gets none of the support from Greece under President Constantine Karamanlis that it did under the former military rulers in Athens.

EOKA-B is drastically diminished. The alleged leader of the six-man kidnap squad, Vassos Pavlides - a violent man implicated in past crimes including his own brother's murder - was the only member of the group still on the wanted list.

In the kidnap bargaining, when a handful of EOKA-B sympathizers who had started out as mediators threatened to distort the process by inject their own demands, the Greek ambassador intervened personally.

Pointing to the condemnation of the kidnaping here and in Greece, a Greek Cypriot commented, "EOKA-B has just enacted its own burial."

While Greek Cypriot political unity was enhanced, the episode was viewed differently across the case-fire line in Turkish-controlled northern Cyprus. The Turkish Cypriot press did not play up the act by the EOKA-B, which has aimed its terrorism at the Turkish Cypriots in the past. Officials commented, however, that the violence was a typical outgrowth of the splits among Greek Cypriots, the Turkish Cypriots sent Kyprianou no message of sympathy.