Bond prices advanced Friday in quiet dealings as the dollar extended its recent gains in foreign-exchange trading. The Treasury's bellwether 30-year bond rose half a point, or $5 per $1,000 in face value, as its yield fell to 8.85 percent from 8.92 percent late Thursday. Analysts said the price increase was due to another rise in the dollar, which has gained ground steadily this week against other major currencies. A higher dollar increases the yields available to foreign investors on dollar-denominated securities, such as U.S. bonds and notes. Most of the gains occurred early in the session, and trading was described as relatively light. In the secondary market for Treasury bonds, prices of short-term government issues rose 5-32 point, intermediate maturities rose by between 7-32 point and 13-32 point and 20-year issues rose ] point, according to figures provided by Telerate Inc., a business-information service. The movement of a point is equivalent to a change of $10 in the price of a bond with a $1,000 face value. The Merrill Lynch Daily Treasury Index, which measures price movements on all outstanding Treasury issues with maturities of a year or longer, rose 0.27 to 110.13. The Shearson Lehman Hutton Daily Treasury Bond Index, which makes a similar measurement, rose 3.01 to 1,153.19. Corporate bonds were little changed. Moody's Investment Grade Corporate Bond Index, which measures price movements on 80 corporate bonds with maturities of five years or longer, rose 0.60 to 284.19. In the tax-exempt market, prices edged up 1-16 point, according to the Bond Buyer Municipal Bond Index. Yields on three-month Treasury bills fell 4 basis points to 6.49 percent. A basis point is one-hundredth of a percentage point. Six-month bills were unchanged at 6.76 percent and one-year bills fell 3 basis points to 6.98 percent. The federal funds rate, the interest on overnight loans between banks, was quoted late in the day at 7| percent, down from 7 9-16 percent late Thursday.