Dec. 1 (Bloomberg) -- Moody's Investors Service may cut the top ratings on six of Citigroup Inc.'s seven structured investment vehicles as part of a review of $130 billion in SIV debt. The net asset value of the $64.9 billion in Citigroup SIVs dropped to below or near 60 percent, prompting the ratings action, Moody's said in a statement yesterday. The junior notes of three of the funds have been downgraded to below investment grade. SIVs, which sell short-term debt to buy longer-term, higher-yielding assets, were shut out of the short-term market as losses on subprime mortgage securities prompted investors to retreat from all but the safest of securities. Unable to finance themselves, three SIVs have defaulted and others are being bailed out by their sponsors. The world's 30 SIVs have more than $300 billion of assets. ``In recent weeks, Moody's has observed material declines in market value across most asset classes in SIV portfolios,'' the ratings company said in the statement. Moody's said it surveyed 20 SIVs since Nov. 7 and expanded its review after noticing ``significant additional deterioration'' in asset values. Moody's cut $14 billion in debt in all, mostly capital notes that rank below commercial paper and medium-term notes and are usually the first to absorb losses, Henry Tabe, managing director in charge of structured finance, said in a telephone interview. The ratings company placed $105 billion of debt on review for a downgrade and confirmed the ratings on $11 billion, Tabe said. Links Finance Corp., a SIV sponsored by Bank of Montreal with $19.1 billion of debt, also had its junior notes cut and may have the remainder downgraded, Moody's said. http://www.bloomberg.com/apps/news?pid=20601087&sid=aRx2AO3552cE&refer=home