The Federal Election Commission is expected to take a step today to resolve the mysterious disappearance of at least $14,000 in contributions from employes of a Las Vegas casino to the 1982 Senate campaign of James D. Santini in Nevada.

Santini, a Democrat who turned Republican to run for the Senate again this year, is caught up in contradictory statements and conflicts over reports to the FEC that have turned the money issue into "a big screw-up," according to Santini's lawyer. The dispute is now before the FEC, which is examining a formal complaint filed by an official of the Nevada Democratic Party.

The controversy dates back to 1982, when Santini, then a Democratic member of the House, waged an unsuccessful primary challenge to then-Sen. Howard W. Cannon (D-Nev.). During the campaign, Santini accepted between $14,000 and $48,000 that could not legally be used in the primary contest because it was from individuals who had already given the maximum allowed under law, $1,000.

These contributions in excess of $1,000, which were made on the expectation that they could legally be used in the general election if Santini had won the primary, were supposed to be given back.

At least $14,200 of these contributions, however, has become the center of an increasingly embarrassing dispute, and Jan Baran, Santini's lawyer, said yesterday that it is not clear what became of the money: "It's a mess and it has to be straightened out."

The issue has also apparently disturbed Santini. Earlier this month, Carlos Harrison, a Las Vegas television reporter, attempted to question him about the money, and Santini ducked away. Film of Santini's response, according to officials of KTNV, was shown on a local news program.

A history of the complex and unresolved dispute over the money, based on interviews and local news stories:

After Santini lost in 1982, his campaign gave at least $13,000 in checks to William G. Bennett, chairman of the board at Circus Circus Enterprises Inc., a casino operator. The checks were to go to Circus Circus employes who had given in excess of the $1,000 primary limit.

These checks, however, went uncashed, leaving at least $13,000 in the Santini campaign fund. At his announcement for the Senate this year and later, Santini said, according to the April 6 Reno Gazette-Journal, "I will stake my life that no representative for me went out and said don't cash those checks."

Last Thursday, however, Bennett, of Circus Circus, issued a statement that appears to contradict Santini:

"Santini told me there was not enough money in the bank to cover the checks, but he assured me he 'would make them good.' I held the checks, awaiting word that sufficient money was available for the checks to be cashed . . . I periodically raised the issue with Santini . . . The only reason the checks were not distributed and cashed was that Jim Santini told me there was not enough money in his account to cover them."

Although all parties agree that the checks have gone uncashed, it is not clear what happened to the money owed Circus Circus employes and to other cash.

In 1983, Santini campaign officials closed out their campaign account, reporting a balance of $561.52 to the FEC. In fact, however, Baran acknowledged that about $22,000 was in the account. This was supported in comments made by Santini's 1982 campaign manager, Robert Henrie, according to local news accounts.

Henrie, who could not be reached by The Washington Post, is quoted by Nevada newspapers as saying that he paid himself between $3,000 and $5,000 and used the rest of the $22,000 to retire campaign debts. Baran, however, said the $22,000 "is something that needs to be cleared up."

While the Democratic complaint against Santini remains unresolved before the FEC, Santini is expected today to get permission from the FEC to use his 1986 campaign fund to pay off the 1982 contributors.

Santini is running against Rep. Harry M. Reid (D-Nev.) for the seat being vacated by Sen. Paul Laxalt (R-Nev.).