By Chris Francescani

NEW YORK, Dec 6 (Reuters) - New York's largest civil liberties group filed a federal lawsuit Thursday against state corrections officials on behalf of a convicted rapist who spent 26 months in solitary confinement after a non-violent offense in his cell.

The lawsuit is the latest challenge to standards by which some 80,000 inmates a day are confined up to 23 hours a day in isolation or with another inmate inside cells as small as a parking spot.

Critics claim solitary confinement is a form of torture that inflicts lasting psychological damage and is meted out in many states too arbitrarily and, increasingly, too often.

New York prison officials declined to comment on the lawsuit but have said in the past it is sometimes necessary to remove inmates from the rest of the prison population.

The lawsuit, filed by the New York Civil Liberties Union in federal court in Manhattan, asserts Leroy Peoples was placed in solitary confinement for nearly 26 months after jail guards discovered forged legal documents in his cell.

Peoples, 30, was sentenced to 16 years in prison after pleading guilty in 2005 to raping two women at gunpoint in Queens, New York, according to prosecutors.

"New York's prison authorities permit the use extreme isolation ... as a disciplinary tool of first resort for violating almost any prison rule, no matter how minor," NYCLU Executive Director Donna Lieberman said in a statement.

Between 2007 and 2011, New York State prison officials segregated inmates 302 times for "smoking in an undesignated area," 135 times for "wasting food," 114 times for "littering" and 234 times for "untidy cell or person," according to a recent NYCLU study of state prison segregation records.

A spokesman for the New York State Department of Corrections said the agency doesn't comment on ongoing litigation. In October, state corrections commissioner Brian Fischer responded to the NYCLU study.

"As a society removes those individuals who commit crimes, so too must we remove from general population inmates who violate the Department's code of conduct and who threaten the safety and security of our facilities," Fischer said in a statement, which did not address non-violent offenses.

"The possession of drugs, cell phones and weapons pose a serious threat within this ... system."

There were 563 assaults on staff and 666 inmate assaults on other inmates last year, out of a population of about 56,000, state corrections records show.

In June, a federal lawsuit was filed on behalf of mentally ill prisoners isolated at Colorado's so-called Supermax prison, and the U.S. Senate held a hearing for the first time to examine the use of isolation in federal prisons.

About half of prison suicides occur in solitary confinement, according to Senate testimony in June from Craig Haney, a psychology professor who has studied prison isolation for 30 years, despite most states segregating less than 10 percent of its prison population.

About 8 percent of New York's inmates are held in isolation, a slightly higher rate than in federal prisons, according to federal statistics.

A 2007 New York state prisons report -- the most recent available -- found 83 percent of New York's prison population showed a need for substance abuse treatment.

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