JAPANESE SEEN LIGHTENING U.S. BOND HOLDINGS The dollar's tumble to a record low of 144.70 yen in Tokyo today motivated some major Japanese investors to lighten their U.S. Bond inventory further and is expected to spur diversification into investment assets including foreign and domestic shares, dealers said. The key U.S. 7-1/2 pct Treasury bond due 2016 fell to a low of 96.08-12 in early Tokyo trade against the 98.05-06 New York finish, then recovered to 96.20-22. Some trust bank pension fund acccounts and investment trusts were seen selling several hundred million dollars on the foreign exchange market here today, accentuating the unit's tumble, securities house dealers said. They seem undecided on what to do with the fresh yen cash positions resulting from their dollar sales today, and are sidelined until the currency market stabilises and the interest rates outlook clarifies, a Nikko Securities Co Ltd currency trader said. The dollar's plunge and low yields on U.S. Bonds will further promote diversification into other foreign investments, as well as call back funds into the domestic bond and stock markets from overseas bond markets, securities bond managers said. They said major Japanese investors in the past two years are estimated to have held 50 to 80 pct of their foreign portfolios in U.S. Bonds but many have lightened their U.S. Bond inventory to as low as 40 pct. Since late last year, Japanese investors, seeking substantial liquidity and attractive yields, have used fresh funds to buy mark and Canadian dollar bonds and, after the Paris currency pact, actively bought French franc bonds and gilts while gradually lightening U.S. Bond inventories, the managers said. Dealers said funds tied up in foreign assets had flowed into local bond and stock markets as well. The yield of the key 5.1 pct 89th bond dropped to a record low of 4.080 pct today from the 4.140 Saturday finish and compared with 4.25 pct on three-month certificates of deposit. The key bond has fluctuated less than five basis points for more than a month here, suggesting most dealers could not satisfy their needs for capital gains, dealers said. A market survey by Reuters showed some active accounts in U.S. Treasuries are currently dealing on Tokyo's stock market. The stock market's bullishness late last week was partly due to funds transferred from U.S. Treasuries, dealers said. Japanese net purchases of foreign securities in the first half of March fell an estimated one billion dlrs compared with average monthly net purchases of 7.7 billion for the whole of 1986, Finance Ministry sources said. The steep fall is due to Japanese investors' cool attitude towards U.S. Bonds, which had amounted to more than 80 pct of total foreign securities purchased, securities houses managers said. Foreign stock buying in March is expected to exceed the record high of 1.5 billion dlrs seen in December, they said. "Diversification of foreign portfolios is underway and we have bought bonds in currencies such as marks, the Canadian dollar, the ECU and French franc," a fund manager at <Yasuda Trust and Banking Co Ltd> said.