The Police: ''Synchronicity'' (A&M Records SP-3735) This British band has, with the release of its newest album, gone from a very good rock band to a brilliant rock band. The Police have successfully blended the distinct styles of the four previous albums to produce this one - the best yet. It has more bite and depth than previous Police records. The unique musical blend that is the Police - new wave, punk, rock, or anything else you'd like to call it - may be slowly entering into a league of its own. The previous success of the band has allowed its three members - singer-songwriter-bassist Sting - that's his full name - guitarist Andy Summers, and American drummer Stewart Copeland - to experiment now with new song styles in music. The current hit single from the album, the jealousy-riddled ''Every Breath You Take,'' is a simple song which, in the hands of the Police, has an unusually powerful impact. Sting's singing is emotional and intimate. The other songs tackle some challenging subjects for a rock band. ''King of Pain,'' one of the finer pieces on the album, is a nightmare-like description of a man's inner struggles. However, ''Mother'' is a strange, rather irritating song by guitarist Andy Summers that should have been left in the studio. The singing is actually painful yelling and screaming. That drumming style of Copeland's has become a trademark - and effectively creates the mood of several songs. The guitar style of Summers pumps a solid, driving beat into most cuts. And Sting's songwriting, bass playing, and singing are superb.