* Obama thanks Sullivan for service
* Director retires after three decades (Updates with Obama statement)
By Tabassum Zakaria
WASHINGTON, Feb 1 (Reuters) - U.S. Secret Service Director Mark Sullivan, whose agency was embroiled in a scandal involving prostitutes in Colombia, will retire this month, a spokesman said on Friday.
Sullivan will step down on Feb. 22 after almost three decades with the agency that protects the president and other officials, Secret Service spokesman Brian Leary said.
"He's got almost 30 years of service so he's retiring. He's the third-longest-serving director," Leary said.
Sullivan joined the Secret Service as a special agent with the Detroit office in 1983 and rose to become director of the agency in 2006.
"I want to thank Mark Sullivan for nearly 30 years of service to our nation at the United States Secret Service, a tenure that saw the agency protect five first families including my own," President Barack Obama said in a statement.
Last year Sullivan went before Congress to apologize for the misconduct of agents who brought prostitutes back to their hotel rooms ahead of a visit by Obama to the Colombian resort of Cartagena in April 2012.
It was the biggest scandal to hit the agency and it set off several official investigations.
A Department of Homeland Security investigation determined that the actions of the Secret Service employees entangled in the prostitution scandal had not compromised the safety of the president or any sensitive information.
Sullivan has been described as polite, hard-working and loyal, and was generally credited with acting aggressively in response to the scandal that tarnished the agency.
"His commitment to keeping our country and its top officials safe is unparalleled, and his devotion to the mission of the Secret Service and Department of Homeland Security has been unwavering," Homeland Security Secretary Janet Napolitano said in a statement.
The Secret Service spokesman would not comment on what Sullivan's future plans were. (Editing by Sandra Maler, David Brunnstrom and Eric Walsh)