The president of Parking Management Inc. and co-owner of a major Washington area construction firm today admitted his guilt to a charge that he willfully evaded paying federal income tax.

John W. Lyon, who in addition to running the Washington area's largest commercial parking firm is president and co-owner of Excavation Construction Inc., pleaded guilty to a charge that he disguised benefits to himself such as yardwork and construction of a swimming pool at his Potomac home by charging the payments to various construction company accounts to avoid taxes. Conviction on the charge carries a possible sentence of up to five years in prison and up to a $10,000 fine.

Lyon appeared in federal court in Baltimore with all the other officers of the troubled construction firm, each of whom entered guilty pleas to tax evasion or conspiracy charges under separate agreements with the federal prosecutor's office.

Under terms of the agreement with Lyon, prosecutors will recommend 120 days' imprisonment and will not object to a defense request that Lyon serve the time on work-release at a community-based facility such as a halfway house.

Lyon, who is also a former director of the National Bank of Washington, was allowed to plead guilty to avoid a trial on several charges of tax evasion and conspiracy. But U.S. District Court Judge Shirley Jones rejected Lyon's request that he be allowed to assert his innocence at the same time he was pleading guilty.

Lyon and his attorney had sought to enter a plea based on a legal precedent that allows a defendant, in effect, to plead guilty without acknowledging guilt.

Judge Jones rejected that notion. The facts laid out by Assistant U.S. Attorney Michael J. Travieso yesterday showed that "this was not an isolated incident. It was the result of a well-designed scheme . . . to evade and defeat the payment of income tax," Judge Jones said.

Under the single count to which Lyon pleaded guilty, he was charged with disguising benefits worth $44,000 on which he should have paid $28,000 in taxes, the judge noted.

"A substantial amount of money is involved even under this one count. . . . all this was done by an educated, experienced businessman who knew what he was doing," Jones asserted.

During the day yesterday, all four major officials of Excavation Construction pleaded guilty to federal criminal charges against them. Larry A. Campbell, general manager and an owner of the multimillion-dollar Prince George's County-based construction firm, also pleaded guilty to a single count of federal income tax evasion.

The government said Campbell had masked $11,000 in corporate expenditures on his behalf to avoid paying $7,900 in federal income taxes. Campbell admitted his guilt, although he and his attorney, Arnold Weiner, said Campbell disagreed with the exact figures.

In the same proceeding, Excavation's assistant general manager and corporate secretary, Robert P. Jenkins, pleaded guilty to having been part of a conspiracy to disguise corporate benefits. Earlier in the day, corporate treasurer Edward W. Storke pleaded guilty to a conspiracy count.

Campbell and Storke will be sentenced Nov. 18, and Lyon and Jenkins face sentencing the following day. Travieso said the government will ask that Campbell serve 60 days and will not oppose a request that he be imprisoned in a community-based facility and placed on work-release.

No sentence was requested for Jenkins, who already is on probation for a 1979 perjury conviction in another case, but Travieso said the government would ask that Jenkins be compelled to pay a fine of not more than $5,000. The government said it would request a fine of not more than $3,000 for Storke.

The guilty pleas appear to cap a four-year investigation and a sea of legal trouble for the construction firm. Started in relative obscurity in 1965, Excavation Construction grew to one of the area's largest heavy construction firms by 1977, when it had $60.1 million in contracts, a huge fleet of red- white-and-blue Mack trucks and was a major Metro subway contractor. In 1979, in the midst of its legal troubles, the firm began reorganizing under federal bankruptcy laws, a process that is still going on.