Sen. William V. (Bill) Roth Jr. (R-Del.) called yesterday for a full-scale Senate investigation into alleged corruption in General Services Administration contracting procedures.

In a letter to Sen. Lawton Chiles (D-Fla.), chairman of the Senate Governmental Affairs Committee's subcommittee on federal spending practices, Roth, a member of the subcommittee, said, "Recent reports suggest the illegal practices involving GSA may be broader than they initially appeared."

Roth was referring to reports in The Washington Post that GSA and FBI investigators have traced more than $2 million in contracts awarded by GSA for repair and alteration work that was never performed.

Although Robert J. Lowry, a painting conractor, began informing GSA of corrupt practices in 1975, the current investigation began only last year.

"The taxpayers are footing the bill for this alleged string of favoritism, abuses of power, and downright fraud," Roth said.

He said hearings would be "beneficial" in focusing attention on the waste of tax dollars, in addition to developing information about how GSA might be reorganized. A government team is currently looking into whether GSA's role should be expanded or diminished.

Roth said the Senate investigation should determine why the alleged practices remained undetected for so long. He said the current executive branch probes should be reviewed to insure that they are thorough , and he said legislation should be considered to prevent future abuses.