The pumping of chlorine dioxide gas into the Brentwood postal facility to kill anthrax spores was completed 12 hours ahead of schedule yesterday, Postal Service authorities said. The gas was being sucked back out of the sealed Northeast Washington building and converted, through chemical treatments, into harmless saltwater.

Thousands of samples will be taken from the building over the next several weeks and tested, a Postal Service spokesman said. An independent committee of scientists will review the results.

If the committee finds no trace of anthrax, it could give a green light for the postal facility to reopen in April -- 18 months after two letters containing anthrax spores passed through the building en route to Capitol Hill, fatally infecting postal workers Joseph P. Curseen, 47, and Thomas L. Morris Jr., 55, with inhalation anthrax.

The sprawling Brentwood building, which once housed 1,600 workers, recently was renamed in memory of Curseen and Morris. It has sat empty while experts designed and tested a one-of-a-kind fumigation system, modeled after the successful decontamination of the Hart Senate Office Building.

The affected area of the Hart Building measured about 170,000 cubic feet; the postal building is more than 170 times that size.

"We are extremely pleased with the results of this process," Thomas G. Day, the Postal Service vice president for engineering, said in a statement yesterday. "It represents a tremendous effort."

Chlorine dioxide, a yellowish-green gas often used to purify water, has been found to effectively kill anthrax spores if concentrated for several hours at 750 parts per million in warm and humid conditions.

Postal Service authorities said that concentration was reached shortly after 7 p.m. Saturday and maintained until about 8:30 a.m. yesterday. At times during the night, a spokesman said, the chlorine dioxide level went up to 1,000 parts per million.

The interior temperature of the building was kept at 75 degrees Fahrenheit, with 75 percent humidity, conditions at which anthrax spores are vulnerable to the gas, authorities said.

Starting yesterday morning, the 25,000-foot network of six-inch pipes that pumped the gas into the building was used to pull the gas back out.

In large tanks at the rear of the building, the gas was treated with salt and sodium sulfate, then pushed through two-foot-thick charcoal filters. In the process, the gas was converted into saltwater and oxygen, the spokesman said.

Although the water is harmless, it was being stored in containers and will be disposed of at a secure U.S. military facility to dispel any public safety concerns, the spokesman said.

Once all the gas is removed, likely by today, work crews will begin drying out the building by using dehumidifiers and blowing in dry air.

Workers wearing safety suits, masks and breathing apparatus also will begin removing 8,000 strips that contain a substance that imitates the growth of anthrax, and 4,000 random surface samples, from the building. The samples will be transported to the Centers for Disease Control and Prevention in Atlanta for testing.

If the building is ultimately ruled anthrax-free, the Postal Service spokesman said, it will take another two months to paint and clean it and install new carpeting. If anthrax spores are found, the building will have to be refumigated.

Though the Postal Service is overseeing the cleanup, a host of local and federal agencies provided support and expertise, including the Environmental Protection Agency. Other agencies involved include the CDC, the Occupational Safety and Health Administration, the National Institute for Occupational Safety and Health, the U.S. Army Center for Health Promotion and Preventive Medicine, the D.C. Department of Health and the D.C. Emergency Management Agency.

The cost of cleaning up Brentwood and another contaminated facility in New Jersey has exceeded $100 million.

Houses and businesses around the Brentwood Road facility were not evacuated during the fumigation, but no one except crews involved in the project was allowed within 282 yards of the building's center.

At the sealed-shut Brentwood postal facility, a fumigation system was set up to pump chlorine dioxide gas into the well-heated and humidified plant. The effort to kill any lingering traces of last year's anthrax attacks lasted several hours, after which the gas was pumped out and converted into harmless byproducts. The plant, which could reopen as early as April, was recently renamed in honor of postal workers Joseph P. Curseen, 47, and Thomas L. Morris Jr., 55, who died of inhalation anthrax after a letter containing spores passed through the facility on its way to Capitol Hill.