Midway Airlines, until now a paper company, announced firm plans yesterday to start low-cost air service from Chicago's "other airport" to Kansas City, Detroit and Cleveland on November 1.

Irv Tague, president of Midway Airlines, said the new Midway Airport service will feature regular, unrestricted air fares 25 to 50 percent lower than those being charged to the same cities by airlines based at busy O'hare International.

Midway Airlines will offer one-class service with a two-tier pricing system pioneered by Southwest Airlines in Texas. Between 7 a.m. and 7 p.m. weekdays the regular fare for all seats will be 25 percent lower than other airlines' current fares; after 7 p.m. and on weekends, the fares will be 50 percent lower.

Five round trips will be flown daily on each route initially, with flights scheduled so that business travelers can make round trips in the same day with ease, Tague said.

The flights will start with three DC9 aircraft leased from Mcdonnell-Douglas; two more leased planes are expected next year. Midway Airlines's also is negotiating for the purchase of five new DC9S for delivery in 1982.

Plans for the service became a reality when Midway Airlines officials wrapped up financing for their venture -- $5.7 million -- on Tuesday.

The announcement was made here in Washington at a press conference hosted by Sen. Charles H. Percy (R III.) and Rep. John G. Fary (D-III.), both of whom have been working to get service back to Midway Airway for several years now.

Once the busiest airport in the world, Midway now sees only three flights a day operated by Delta Airlines, the lone airline that stayed on with minimum service when everyone else moved to O'hare.

Besides the money to be saved by travelers using Midway Airline's lower fares, Percy cited potential savings of fuel as the number of travelers using Midway grows, reducing traffic around O'hara Airport and therefore the amount of time planes spend circling and waiting to land. As for passenger convenience, point-to-point travelers not needing connecting flights will find it quicker to get to downtown Chicago from Midway, he said.

Percy also cited the certain rejuvenation of the economically stagnant southwest side of Chicago where Midway Airport is located as off-airport businesses and jobs are created. Initially, Midway Airlines plans to hire about 200 persons with an annual payroll of $4.2 million. CAPTION: Picture, Midway Airlines President Irv Tague and Sen. Charles Percy with airliner model carrying Midway Airlines markings. By James K. W. Atherton -- The Washington Post