Senator Howard Metzenbaum (D-Ohio) yesterday disclosed that a Republican lobbyist had a secret stake in a Texas savings and loan whose sale is the target of a widening Senate investigation.

Metzenbaum said documents recently obtained by a Senate subcommittee show that Washington lobbyist Robert J. Thompson "claimed to be entitled to a 2 percent share" of Bluebonnet Savings Bank of Dallas, which is receiving $1.85 billion in federal subsidies, a deal Metzenbaum says is "the worst case we have found" of abuse in the S&L bailout.

Metzenbaum yesterday began efforts to subpoena records of Thompson as well as James Fail, the Arizona businessman who acquired Bluebonnet, some business associates of Thompson and Fail and federal regulators involved in the transaction.

Thompson worked on George Bush's vice presidential campaign in 1980, served as an aide to the vice president and then left the government to set up a lobbying firm, Thompson and Co.

Metzenbaum, the New York Times and Cable News Network have disclosed that Thompson lobbied federal regulators on behalf of Fail, who failed to disclose legal problems that might have disqualified him from buying a financial institution. In addition to Bluebonnet -- an amalgamation of 15 failed thrifts obtained from the Federal Savings and Loan Insurance Corp. -- Fail also took over an insolvent Oklahoma bank with aid from the Federal Deposit Insurance Corp.

Thompson was not only a paid lobbyist for Fail in the Bluebonnet transaction, but also had a previously undisclosed stake in the deal, Metzenbaum said yesterday. "We believe this interest to be worth millions of dollars," he said in a statement. "Until recently, we had no reason to believe that Mr. Thompson has such a personal stake in seeing the deal go forward."

Aides said they could not elaborate on Metzenbaum's statement about Thompson's stake in the project. Thompson could not be reached for comment last night.

Metzenbaum said Thompson has provided some documents sought by the Senate antitrust, monopolies and business rights subcommittee but on Monday balked at providing further information to the panel, which Metzenbaum chairs. Sen. Orrin Hatch (R-Utah) said he understood that Thompson was willing to cooperate with the subcommittee but objected to having his financial information leaked to the press.

The subcommittee voted to subpoena records of Thompson and Fail, but said serving the orders would be delayed while staff members tried to get the records voluntarily. It agreed to issue subpoenas for Thomas Lykos, a former FSLIC official, and Robert Pennington, former president of Mutual Security Life, an insurance company controlled by Fail, seeking their testimony.