Federal Aviation Administration officials have launched a study of two recent test-flight accidents of the McDonnell Douglas DC9 Super 80 that could delay certification and deliveries of the new plane that are scheduled to begin in July.

No one has been injured in the accidents, both of which occurred during strenuous landing tests that exceed normal operating limits. Nonetheless, "We have to assure ourselves that there was nothing deficient in the design" of the airplane before it can be certified, said Tony Broderick of the FAA's airworthiness office.

Senior FAA engineering officials will travel to Los Angeles next week to discuss the accidents with both FAA and National Transportation Safety Board investigators, it was learned.

"We don't know whether this will take six hours, six days or six weeks," said Broderick, "but there is certain to be some delay."

The landing accidents are bad news for McDonnell Douglas, which has 86 confirmed orders and 28 conditional orders for the Super 80. Douglas officials have hoped that strong sales and good performance in the first year of operation for the airplane would help restore luster to the company's image after the highly publicized DC10 crash in Chicago in May 1979.

John Cooke, spokesman for McDonnell Douglas, said "I understand there are some FAA people coming out, that would be a perfectly reasonable thing for them to do." However, Cooke said, there was no suggestion that the FAA check would in any way be a formal suspension of certification proceedings. FAA officials agreed with that analysis.

Before an airplane can be placed in service, the FAA must find that the craft is "airworthy." After that determination is made, the plane receives a "type certificate." Only then can the plane be flown in commericial passenger service.

The first DC9 Super 80 is scheduled for delivery to Swissair. Foreign air safety agencies normally honor FAA certification and, in any case, would not accept the Super 80 for their own airlines if the FAA would not accept it for U.S. carriers.

The first accident occurred May 2 at Edwards Air Force Base, Calif. The Super 80 made a "hard" landing, which means it was intentionally landed overweight and with less care than would be normal. The plane's tail, vital for control in flight, separated from the rest of the fuselage.

The second accident occurred June 19 at Yuma Airport. The plane was simulating the type of landing that would be made if there had been a major failure in the hydraulic system. Therefore, none of the devices on the wing that normally are used to slow speed and stabilize the plane were employed. The plane hit the runway at a much higher speed than normal because of that configuration.

According to an early report from the safety board, the aircraft veered to the left; the pilot braked the right landing gear to correct and the tires blew; the pilot braked on the left side and the left gear tires blew; the plane veered back to the right, left therunway and came to rest facing the wrong direction. Although all three landing gear components were destroyed, the fuselage was intact.

The DC9 Super 80 sells for about $50 million and will carry as many as 178 passengers, although a normal seating arrangement would be for 155. It is a "stretched" version of the present DC9 but has much quieter engines and carries 25 to 50 more people.

Cooke said that "I don't think we have seen any softness in our orders because of these incidents. The airlines realize that they occurred when the airplane was way out on the edge of the flight envelope."