A 60-year-old Virginia man, detained at the Northern Virginia Mental Health Institute under a court order, walked through an unlocked door Wednesday, hailed a cab and rode away.

After searching for two hours, a Fairfax County police patrol found the man hiding at an Arlington Boulevard dentist's office six miles away. He was captured without incident and returned to the faculty at 3302 Gallows Road, Fairfax County, an "open door" state psychiatric hospital.

Four hours later, the man, believed by a member of the institute's staff to have suicidal tendencies, escaped again -- through the same door. He was captured in Arlington County Thursday.

There have been 131 escapes from the institution this year. Of the people held at the institute this year while a court-appointed magistrate determined whether they were "a danger to themselves or to others, or unable to care for themselves," about one quarter walked away.

The ease and frequency of those escapes have drawn complaints from the institute's neighbors and from Fairfax County police charged with searching for the escapees.

An official of the Dominion Psychiatric Treatment Center and Barcroft Institute said the escapees occur because the Northern Virginia Mental Health Institute is an "open ward, least restrictive facility" that is not designed to detain patients.

"That's an embarrassing problem," said Dr. Martin Stein, director of the Dominion center. "It's unreasonable to send a person who is to be detained to an open ward facility. It's a real problem. The court has asked us to accept some of the people because they are really hard up."

The state-funded Northern Virginia institute and the Dominion center are among six facilities used by the Fairfax court system and other Northern Virginia jurisdictions for the detentions.

But there have been only two escapes in the past three years from the Dominion center -- a locked facility -- and the psychiatric wards of Fairfax and Mount Vernon hospitals, both of which are described as "secure" by police.

A person who lives near the institute and works in the psychiatric ward of Fairfax Hospital complains that people "escape from the institute on almost a daily basis. Some are suicidal. Some have threatened their families with weapons. If they decide to leave, they just walk out, and that's crazy."

The institute's director, Dr. Robert E. Strange, said he can understand the concern generated by the escapes, but added that "we're an open part of the (state mental health) system. The institute is not geared for closed-ward care."

The 11-year-old, 120-bed institute, said Strange, was designed to give patients "relative freedom, with responsible behavior emphasized to facilitate (the patient's) return to the community."

But Strange added, "Our patient load is becoming more difficult. We've got some pretty sick people here. The larger state facilities are cutting down on their patient numbers." He added that patients the institute considers dangerous are observed every 15 minutes.

Judge Robert M. Hurst, Fairfax County's chief district court justice, said the detainment procedure begins when a family member or doctor calls the court to report suicidal, threatening or irrational behavior in an individual.

Those detained for 24 to 48 hours pending hearings before a special magistrate are frequently the most disturbed persons in their communities and more than half were previously committed to state hospitals, according to a 1978 study. "We spend a considerable number of man hours when we have to round up these people," said Fairfax Police Capt. Charles Cooper, whose Mason District officers search for the escapees. "Then there is all the paperwork that has to be done. "Some of (the escapees) hitchhike, some take off in buses. You never know what they're going to do. It's just fortunate that all have been returned without incident."