COLUMBIA, S.C., JULY 20 -- A federal grand jury today demanded campaign spending records from all 46 state senators, expanding the scope of an investigation into allegations that lawmakers traded votes for cash.

FBI agents delivered the grand jury subpoenas to the Senate Ethics Committee two days after asking for similar campaign records from all 124 House members. Those records were turned over Thursday.

The probe involves an FBI sting operation in which a lobbyist working undercover offered legislators cash in exchange for votes on parimutuel betting legislation in the General Assembly. Agents videotaped some lawmakers accepting money, a source who requested anonymity told the Associated Press.

"It will cut deep -- both parties are involved. . . . It crosses everything," an unidentified source told the Charlotte (N.C.) Observer.

The newspaper reported that sources called the probe one of the Justice Department's top white-collar investigations this year.

The investigation apparently involves possible violations of the Hobbs Act, a federal anti-corruption law banning acceptance of money or gifts in return for votes or other favors.

U.S. Attorney Bart Daniel and Fred Verinder, the FBI's top agent in South Carolina, confirmed only that an investigation was underway into allegations of "illegal conduct involving certain members of the South Carolina Legislature."

"There will be no further comment until charges are filed," they said in a statement.

Ron L. Cobb, a former House member-turned-lobbyist, is at the center of the probe, according to lawmakers. They said Cobb offered at least three legislators money in exchange for their help on a bill that would have allowed parimutuel betting in South Carolina. The General Assembly failed to act on the measure before adjourning in June.

Cobb, who served in the House from 1977 to 1984, did not return telephone messages.

Among Cobb's clients is Alpha Group, an Atlanta-based concern interested in promoting parimutuel betting in South Carolina.

Campaign contributions to legislators from Cobb, Alpha Group and Cobb's company, Government Business Associates, totaled at least $12,950 since 1987. Contributions ranged from $100 to $3,000.

State Rep. Paul Derrick (R), who accepted $1,000 from Cobb in a Columbia motel room earlier this year, said he now believes the cash payment was part of an FBI sting. He said Cobb did not ask him at the time for his vote on parimutuel betting, but the lobbyist had earlier sought his support for that bill.

Rep. Ennis Fant (D) said he also discussed parimutuel betting with Cobb, who told the lawmaker, "Let me give you a little gas for your tank," and produced $1,000 from his briefcase. Fant said he accepted two cash contributions totaling $1,300 from Cobb in March or April and reported them on his ethics disclosure forms.