Low-fare air travel options are enhanced for Washintonians this week with the beginning of new services by Midway Airlines to Chicago and World Airways to London via Boston.

Midway, the first airline to be formed under the Airline Deregualtion Act, began services between Chicago's Midway Airport and three midwestern cities last fall. This week, it begins offering Washington-area travelers the same ease of getting to Chicago witout going through congested O'Hare that increasing numbers of travelers from Cleveland, Detroit and Kansas City have come to enjoy.

Midway users also get a price break: Midway's one low fare from Washington -- $85 on all seats on all flights -- is 30 percent below the normal coach fare of about $123 its major competitors offer. The firm intends to maintain that price differential, too. Midway will be operating four roundtrip flights a day out of National Airport at times that allow business travelers to leave in the morning, spend a day in the other city working and be back at night.,

For the first two weeks of its service -- unitl June 15 -- Midway is off offering a one-cent sale. Until the 15th, passengers who buy a regular $85 one-way ticket will be able to purchase the return trip ticket for one cent., The return trip, in either direction, can be made anytime during the month of June. Tickets for the introductory sale will be available only at Midway's ticket counters. At National, Midway is operating out of the American Airlines terminal and gate areas.

Midway has been carrying increasing numbers of passengers each month since it began operations and expects to begin reporting profits next month, according to Kenneth Carlson, vice president of marketing. For Carlson, who owns a farm in Virginia and had worked in Washington four years before moving to Chicago last year, the new Washington service represents more than a business opportunity.

"It's kind of fun to come home with your own airline," he says.

This week, it begins new low-fare service to London with a stop in Boston, its official gateway to Britain. World's summer fares to London are about 40 percent lower than comparable reserved-seat competitive fares. The service operates from BWI three times a week.

World's regular summer fare, for a reserved coach seat with meal service, is $300 each way. In comparison, a regular coach seat on Pan American World Airways this summer is $470 each way with an increase expected soon.

World's regular round-trip fare is even cheaper than Pan Am's advanced purchase excursion fare of $660.

World is offering an introductory one-way economy fare of $200 to London between now and June 18, and a $400 round-trip fare for travelers who leave before June 18 and return on or before June 30. After the summer peak travel season is over, World's fare will fall to $250 each way.

World will offer a year-round one-way commuter fare of $50 between BWI and Boston.