The primary general contractor for the $8.5 billion CityCenter project on the Las Vegas Strip plans to sue the project's owners for $492 million.

Casino operator MGM Mirage , which owns the multi-tower site in a 50-50 partnership with Dubai World , disclosed the threatened mechanics' lien in a filing to U.S. regulators on Friday.

A spokeswoman for Perini Building, the Tutor Perini Corp unit which was the primary general contractor at CityCenter, said the company did not want to comment on the filing.

MGM, based in Las Vegas, said the actual lien may be filed within 15 days of the notice.

A mechanics lien is a lien against buildings or other structures allowed by some states to contractors, laborers and suppliers of materials used in their construction or repair.

CityCenter believes that its actual obligation to the general contractor is substantially less than the amount claimed and that it is also entitled to significant offsets against the claimed amount, MGM said in its filing.

The company intends to pursue all of its rights and remedies, including arbitration. Meanwhile, the CityCenter joint venture has obtained a six-month amendment to its $1.8 billion credit facility that would allow for additional construction liens.

Because the general contractor may be able to file liens on CityCenter for more than what CityCenter's fully drawn credit facility allowed, CityCenter obtained an amendment to the credit facility that allows for additional construction liens in an amount more than sufficient to cover the threatened liens, according to the filing.

MGM also said it believes it has significant claims against the contractor in connection with construction defects at CityCenter's Harmon Hotel tower.

The Harmon, one of the site's six major components, was designed as a 49-story condominium hotel, but the height was halved after it was discovered that reinforcing bar had been improperly installed on some floors.

CityCenter, with its flagship Aria casino-hotel, opened in December in something of a victory for highly-leveraged MGM, which had come close to defaulting on its debt as the recession pummeled gambling demand.

Shares of MGM, which closed at $11.80 on the New York Stock Exchange, were down a fraction at $11.73 in after hours trading.

(Reporting by Deena Beasley; editing by Andre Grenon and Carol Bishopric)