Billie Sol Estes, the Abilene boy-wonder promoter of the early '60s who pyramided a fradulent empire of nonexistent anhydrous ammonia tanks and various land and cattle schemes into a $150 million fortune, pled guilty yesterday to one count of conspiracy to defraud the government, which could send him back to prison for five years.

Estes served six years of a 15-year sentence, beginning in 1965, for the multifaceted '60s fraud case and since 1971 has been on parole.

U.S. District Court Judge Eldon Mahon yesterday accepted Estes' guilty plea, which came after months of plea bargaining with U.S. attorneys, and two years of investigation by a variety of federal agencies, including the FBI, Internal Revenue Service, Postal Service and the Securities and Exchange Commission.

Mahon said he needed to study the presentencing report of Estes' parole board before deciding on a sentence.

Estes admitted guilt in amassing several businesses and real estate holdings while hiding the ownership under friends' names, to moving money that had been obtained by false and fraudulent pretense across state lines, and lying to the IRS about his assets.

He admitted to the judge that it was all done to keep the IRS from learning that he had such assets.

He owes more than $30 million to IRS from his prior business dealings.

Though it was not mentioned in yesterday's court proceedings, any business activity on Estes' part was prohibited by his stringent 1971 parole agreement.

The government's conspiracy case charged that Estes and two business associates, Raymond K. Horton and Buster Lea, met and planned how to accumulate various properties for Estes, using Horton's name.

These businesses allegedly included a motel, a cattle company, a private club, a ranch, apartment complexes and various other pieces of real estate.

Yesterday's 55-minute appearance by Estes in federal court here came unexpectedly, and only 18 persons were in attendance.

Prosecutors and defense attorney G. Brockett Irwin of Longview, Tex., had met until midnight arguing the plea bargain arrangement. The government was ready to go to a federal grand jury to obtain a four-count conspiracy and fraud indictment - which, on conviction, would carry a maximum sentence of 73 years - if the bargain had not been struck.

Estes won two major points in the plea bargaining. The government recommended - and Mahon accepted - that Estes' brother, Dr. John L. Estes; his daughters, Pamela Tedford and Patsy Estes; son-in-law Walter Tedford; and his former Secretary, Sue Goolsby, not be indicted or investigated further. All reportedly had had important roles in the buying, selling and promoting of the Estes' properties.

The second is that the government agreed it would not oppose any parole opportunities for Estes and would not oppose his serving any new sentence at the same time he is finishing his time on parole from the first offenses.

Estes, a bit pauncher than in his heyday of the '60s, appeared subdued as Assistant U.S. Attorney Jim Rolfe read a 16-part stipulation of evidence. Estes then told the judge he pled guilty because, indeed, he was guilty and he waived further proof of the stipulated case against him.

Mahon asked him 17 times if he understood the plea and if he had no threats, intimidation or coercion in doing so.

Each time Estes meekly replied, "yes, sir."

Estes, 52, was released on his own recognizance. His wife and two of his four daughters were in the front row.

Estes' illegal activities of the '70s paralleled those which led to his imprisonment in 1965. Investigators for several federal agencies claim that as late of 1976 Estes controlled 17 different businesses. Allegedly, in most cases, after investors plowed money into the firms, the assets would disappear and the firms would be bankrupted.

In one instance, reiminiscent of the anhydrous ammonia tanks against which he borrowed heavily in the early 1960s but which existed only on paper, Estes helped gather $528,000 in loans from three investment companies against 36 automative steam cleaning machines that he allegedly owned. Only one completely built machine was found.

In another unusual arrangement, Estes bought several welding machines for which he never paid. He resold them to a leasing company and then arranged for their lease to a San Angelo, Tex., trade school at a rate four times their worth.

The government charged also that Estes' employment at Permian Petroleum Corp. where he claimed to be a $700-a-month dispatcher, was part of the fraud and was actually a base of operations for merging other companies in and out of several of the shell firms.

Estes caused the government considerable embarrassment last May, when he tape recorded a telephone conversation between Assistant U.S. yers, Jack Bryant of Abilene. In the chance to plead guilty to one count and promised him that if he did, the government would not continue to investigate his family and former secretary.

At the same time Bryant was told that if Estes pled guilty Bryant also would be free of a possible conspiracy indictment.

At the time Estes was adamant about the offer, calling it "the worst kind of blackmail."

"What would you do?" Estes said, "if they told you they were going to indict your brother, your daughters, and your long-time secretary? What would you do?

"I'll bet President Carter wouldn't like this if he knew how they were blackmailing people. Is this Russia or is this the United States?"

That outburst, made to Texas news papers, caused considerable negotiation and several meetings between Estes, his defense lawyer Irwin and Justice Department officials in Dallas and Washington.

In essence, however, that was what Estes finally accepted.

Rolfe and U.S. Attorney Ken Mighell appeared yesterday for the government.

Estes met briefly with parole officials before slipping out the back door of the courthouse where he waved and smiled to some reporters he had known over the years. He refused all comment.