Hundreds of thousands of people seeking Social Security disability benefits would be required to take an exercise test under rules that the Bush administration plans to release soon.

Critics led by Sen. David Pryor, D-Ark., contend the test is unreliable. They cite a federal appeals court's finding last year that the test often fails to detect one of the most common cardiovascular disorders.The test requires applicants to pedal a cycle or walk on a treadmill whose speed or slope is increased. Those who pass the stress test may be declared ineligible for the benefits.

The administration expects thousands of people - who would now qualify for disability benefits averaging about $550 per month - to be eliminated by the test. The government would save about $40 million in the first year, and $220 million a year by 1995.

The Social Security Administration already uses the test in many cases to assess an individual's heart condition. The new regulations would require a treadmill test for every applicant with heart disease who could safely undergo one.

Social Security expects to publish the new regulations this summer, said spokesman Philip A. Gambino. They then would be subject to a 60-day public comment period.

Officials say the test would be used only in conjunction with a series of other medical procedures that would act as a backstop to guard against false results.

But the Senate Special Committee on Aging, of which Pryor is chairman, said Friday that Social Security "appears to be ignoring the medical evidence" by increasing reliance on the tests.