Here are provisions of the drought relief bill that President Reagan signed today. The new law: _ Authorizes $3.9 billion for relief for drought-stricken farmers. _ Provides payments for farmers who lose more than 35 percent of their crops because of drought, hail, excessive moisture and related problems. _ Furnishes 65 percent of income lost from damage to the portion of the farmer's harvest exceeding the 35 percent level, and provides 90 percent of income lost from damage to the portion of the crop exceeding the 75 percent level. _ Combines two existing livestock feed assistance programs and streamlines machinery for making it available to farmers who otherwise would produce their own feed. _ Caps benefits at $100,000 for each individual. Bars benefits for those with $2 million or more a year in gross farm income. _ Requires that those who receive crop loss benefits must purchase federal crop insurance next year if their losses this year total more than 65 percent. _ Provides that farmers will not have to return income-support payments received in advance if their losses represent less than 35 percent of their crop. This helps producers whose payment level has been lowered by drought. _ Requires producers receiving disaster benefits on 35 percent to 100 percent of their crop to repay these advance income-support, or ``deficiency,'' payments but not until July 31, 1989. _ Blocks an increase of 50 cents for each 100 pounds of weight in the dairy price-support level that was scheduled for January. Increases the level by 50 cents a hundredweight for April, May and June of next year. _ Allows the Agriculture Department to sell corn to ethanol producers at reduced prices but limit participation to producers who use no more than 30 million bushels of ethanol annually. The secretary of agriculture is free not to implement the program.