An Army warrant officer, said to have been within a month of retiring from the military, and five Thai nationals were arrested yesterday on charges of trafficking in what law officials said was some of the purest heroin ever smuggled into the United States from Southeast Asia.

The arrests followed two undercover purchases in May of 33 ounces of heroin believed to be 90 percent pure and worth $2 million on the street, a spokesman for the Drug Enforcement Administration said. They were the first arrests in the Washington area made by the President's Organized Crime Drug Task Force, a $127 million cooperative effort by the DEA, FBI, Customs Service and the U.S. Attorney's Office aimed at major traffickers thought to be involved with organized crime.

A spokesman identified those arrested yesterday as Chief Warrant Officer John A. Davis, 38, and his Thai-born wife, Vundee Klueymai Davis, 41, both of 3903 Old Bridge Rd., Woodbridge; Pronchai Phershayaphai, 33, and Rarai (Monica) Mendell, of 3000 Furman La., Alexandria, and Sunt Mongkol, 39, of 3514 Randolph Rd., Silver Spring.

Also arrested in Los Angeles in the case, a DEA spokesman said, was a Thai man known only as Yon.

The five arrested in the Washington area were charged with conspiracy, smuggling, possession and distribution of heroin. They were arraigned in U.S. District Court in Alexandria and bond for four of them was set at $1 million each. Bond for Davis' wife was set at $2 million.

Officials at Fort Belvoir, where Davis was assigned, said yesterday that he was a project officer assigned to an engineer training brigade. A spokeswoman said Davis had been there for about one year and that before his arrest he was on "terminal leave," due to retire from the Army in one month. The spokeswoman declined to say how long Davis had served in the Army.

The arrests were said to have followed a purchase of nine ounces of heroin on May 11 for $37,500 in Northern Virginia, and 24 ounces more for $120,000 two weeks later.

"The size of the arrest was significantly above average and we don't see heroin of this purity and quality very often," said David Westrate, special agent in charge of the DEA's Washington office. "We invested significant time and resources into this one because of the purity of the drug," which was imported from Thailand.

Westrate said the arrests will have an effect on heroin trade in the Washington area, and on markets as far away as Los Angeles, where the investigation began three months ago.

DEA special agent Ken Cloud would not disclose how the heroin was smuggled into the country, nor would he say under what conditions the purchases were made. "The investigation is still continuing," he said.

"I would say that these were significant arrests," Cloud said. "When you talk about a military man being involved in smuggling drugs into the U.S., that is significant."