The three arrested men are former general security chief Jamil al-Sayed, ex-military intelligence boss Raymond Azar and former internal security head Ali al-Hage, according to security sources.
The head of the presidential guard Mustafa Hamdan has also turned himself in to UN investigators after Lebanon issued an arrest warrant against him.
The men were arrested at the request of UN investigators probing the killing of the former prime minister, who was killed along with 20 others in a massive bombing in Beirut.
Several other people were also arrested by Lebanese police and a warrant has reportedly been issued for former pro-Damascus minister and MP Nasser Qandil.
They are the first major arrests in the probe.
Mr Sayed was widely regarded as Lebanon’s most powerful security figure between the end of the civil war in 1990 and Syria’s pullout of its forces earlier this year.
Mr Hamdan, who was appointed by Damascus protégé President Emile Lahoud shortly after he took office in 1998, was in June questioned as a suspect and his office and house searched by the UN team investigating the murder.
All the men have been previously questioned.
It is not clear whether they will be charged.
Mr Hariri’s death plunged Lebanon into turmoil and increased the pressure on Syria to pull out its troops in April.
Syria has faced mounting international criticism over its perceived failure to cooperate with the UN probe, headed by German prosecutor Detlev Mehlis.
Syria has denied this as well as any involvement in Mr Hariri’s death, but vowed to fully cooperate with the investigation.
Mr Mehlis is due to report on the progress of the case to the UN Security Council in the next few weeks.