Olga Thrasher, wife of an alleged marijuana kingpin in southwest Virginia, pleaded guilty yesterday to helping one of her husband's associates elude authorities, then plotting the man's abduction after she grew suspicious of his loyalty.

Her pleas, entered in a state court in Wytheville, Va., and a federal court in Roanoke, marked the latest phase in a drug investigation that has preoccupied narcotics investigators there for the past six months.

The investigation, which first focused on Thrasher's husband, Wallace, who disappeared in November, expanded to include Olga Thrasher after a series of events that defense attorneys and prosecutors alike describe as bizarre.

Assistant U.S. Attorney Richard Pierce in Roanoke said yesterday the 28-year-old mother of two acknowledged telling an informant that her husband "had been flying planes for drugs for years and she planned to continue the business" after his disappearance.

She also acknowledged in government papers submitted to the court "that neither she or her husband had any substantial legal source of income for at least the preceding five years," Pierce said.

Her guilty pleas yesterday were part of an overall agreement between her defense attorneys and federal and state prosecutors in Virginia and Florida.

She pleaded guilty to a federal charge of aiding Nelson King, who investigators believe was the pilot for the drug ring, after King's plane crashed in Carroll County, Va., last Oct. 17.

She also pleaded guilty to violating a U.S. currency statute in the cash purchase of an $85,000 town house with 10 cashier's checks of less than $10,000 each. Pierce said the arrangement caused a Virginia bank to fail to report the cash transactions, as required by federal law.

In state court, she acknowledged her guilt on state charges of conspiracy and solicitation to abduct King a month and a half ago in Florida.

As part of the plea arrangement, she also agreed to testify for the government in King's upcoming trial on drug-smuggling charges.

In return, state prosecutors in Virginia and Florida agreed to drop charges that she plotted to have King killed. Wythe County Commonwealth's Attorney Thomas Baird Jr. agreed to recommend a sentence of 18 months' probation on the state charges.

Federal prosecutors agreed to inform the court at sentencing of her cooperation in the case against King. Thrasher faces a possible sentence of 7 1/2 years and a $66,500 fine on the federal charges.

The drug investigation was launched after a small plane laden with 570 pounds of marijuana crashed just below the crest of Fancy Gap Mountain on Oct. 17.

One man died in the crash. Authorities allege that King, 38, walked away from the wreckage and called Wallace Thrasher, who owned the plane, for help.

Thrasher, 44, drove King to the Thrasher's home in Bland County, according to court papers filed yesterday.

There, prosecutor Pierce said, Olga Thrasher "helped patch him up and assisted in getting him ready to flee to Florida."

Shortly after the incident, Wallace Thrasher vanished.

Olga Thrasher told authorities that her husband was dead, but law enforcement officials contend a death certificate filed in a Florida state court is fake. The certificate attributes Thrasher's death to another "tragic" plane crash in Jamaica on Nov. 5. Federal authorities have issued a sealed warrant for his arrest.

In February and March, authorities have alleged, Olga Thrasher tried to hire a man who lived in her guest house to abduct and murder King. According to prosecutors in Virginia and Florida, she apparently believed King had played a role in her husband's death and had bilked the couple out of $250,000 in drug money.

King, who was arrested shortly before the murder allegedly was to take place, faces federal charges of drug trafficking and possession with intent to distribute the bales of marijuana found in the wreckage of the plane. His trial is set for May 16.