Maryland Gov. Harry Hughes said today that he will ask U.S. Secretary of Agriculture John R. Block to designate all 23 of the state's counties as disaster areas because of the severe drought that has hit the region this summer.

The letter making the request--the first step in getting low-interest relief loans for farmers--will be delivered to Block in Chicago on Friday by state Secretary of Agriculture Wayne A. Cawley.

Last month, Hughes had asked Block to declare six Maryland counties disaster areas but after a statewide aerial tour by Cawley, he said he decided to make the request for the entire state except the city of Baltimore.

"What Secretary Cawley saw from the air was even worse than we had anticipated," Hughes said.

The governor and his staff expect the request will be granted with little trouble. The major criterion for qualification for disaster relief is the loss of 30 percent of a given crop. Many Maryland farmers report they have lost more than 50 percent of their crops, the hardest hit being corn, tobacco and soybeans.

If the relief is granted, farmers in the state would qualify for long term loans at about 50 percent of the current loan rate, or about 8 percent.

On other topics at his press conference today, Hughes said that with income tax revenues for fiscal 1983 $11 million under estimates, he will consider pushing legislation to restructure the state's income tax system.

If Hughes does seek a change he is likely to meet opposition from the legislature, most notably Speaker of the House of Delegates Benjamin L. Cardin, who is vehemently opposed to any change. Hughes said he would meet with legislative leaders in a few weeks before deciding what to do.

Hughes said that in spite of Wednesday's announcement that 9,500 hard-core unemployed Marylanders would lose their benefits before the end of this month, he is not likely to support legislation to extend the state's participation in unemployment benefits, noting that Maryland already goes further than most states in this area.

Hughes said, however, that he plans to go to Hagerstown and Cumberland soon to discuss employment strategies with business leaders in those two recession-hit cities in Western Maryland. The two face a total of 1,500 layoffs in the next few months because of the shutdown of plants by Kelly-Springfield in Cumberland and Fairchild Industries in Hagerstown.