NEW YORK (Reuters) - A former New York lawyer convicted of helping a jailed Egyptian militant cleric smuggle messages out of prison lost her bid on Friday to be released from prison because she is suffering from terminal cancer.

Lynne Stewart, 73, is three years into a 10-year prison sentence after being convicted of aiding her client, blind cleric Sheikh Omar Abdel-Rahman, who was convicted in 1995 of conspiring to attack the United Nations and other New York City landmarks.

Stewart, known for her advocacy of left-wing causes, is suffering from stage IV breast cancer and asked that her sentence be vacated or modified to time-served.

U.S. District Court Judge John Koeltl denied Stewart's request, noting that the Federal Bureau of Prisons recently denied her application for compassionate release.

The Bureau of Prisons must agree before a court can reduce a sentence based on compassionate release, he said in court documents.

However, the judge left open the possibility that she might still have a chance at freedom, saying that in the time since the Bureau turned her down, her doctor said she has less than 18 months to live.

Stewart's attorneys have resubmitted her application with the Bureau, and it is pending, Koeltl said.

He said the court was "prepared to give prompt and sympathetic consideration" to a motion by the bureau seeking compassionate release.

A federal jury in New York convicted Stewart in 2005 of helping Abdel-Rahman smuggle messages to Egypt's Islamic Group, which in the 1990s waged a bloody campaign against security forces with the aim of creating an Islamic state but later renounced violence.

Stewart was sentenced to 28 months in prison, a sentence that an appeals court later deemed insufficient. In 2010, she was re-sentenced to 10 years in prison.

Stewart was first diagnosed with breast cancer in 2005, and it returned last year, according to court documents. The cancer has spread into her lungs and lymph nodes, and she needs help bathing and suffers from the side effects of chemotherapy treatments, the documents said.

(Reporting by Ellen Wulfhorst; Editing by Cynthia Johnston and Carol Bishopric)

[Image: 73-year-old former New York lawyer who was convicted in a terrorism case, outside of a U.S. District Court in Manhattan, New York on Aug. 8, 2013. By Stephanie Keith for Reuters.]