WASHINGTON (AP) _ The maker of a light helicopter popular with police departments and flight training schools says the government should not ground the aircraft for safety questions. The company blames pilots for crashes.

The National Transportation Safety Board has asked the federal government to ground the Robinson R22 helicopter, which came on the market in 1979, and a newer model, the Robinson R44, until experts can figure out what caused four crashes that killed seven people in Germany, Switzerland and the United States last year.

``This was completely uncalled for,'' said Frank Robinson, president of Robinson Helicopter Co. of Torrance, Calif., manufacturer of the R22 chopper. ``It has no problem as long as there's an experienced pilot at the controls.''

In each case, investigators suspect malfunctioning rotor blades, the NTSB said in a letter delivered Friday to the Federal Aviation Administration.

In at least three cases, the blades hit the main bodies of the helicopters or sliced off their tails, the letter said.

``Anomalies in the main rotor system or cycle control in the cockpit may have gone undetected during the original certification process,'' the letter said. ``Because the recent German R44 accidents occurred abruptly and with no apparent warning to the flight crew, they are of particular concern to the safety board.''

The FAA said it was studying the NTSB's concerns.

``We did receive the recommendation today, and it is under review as we speak,'' said Debra Myers, an FAA spokeswoman in Fort Worth, Texas.

The NTSB makes recommendations to the FAA. It is up to the FAA to decide whether to put them into action.

``They didn't find anything wrong with the helicopter in any of those accidents,'' Robinson said. ``In each case, the pilots presumed to be on the controls _ either a student or a solo pilot _ were very inexperienced. And in several of the cases they were flying in severe weather conditions.''

Robinson also said the chopper is used by 80 percent of all flight schools worldwide. ``So it gets a very high exposure to very inexperienced and, in many cases, poorly trained pilots,'' he said. ``It actually has the lowest accident rate due to aircraft mechanical function of any of the light helicopters.''

The NTSB said it is aware of 339 accidents that have occurred in the United States involving the R22. Three R44s _ which came on the market about 1 1/4 years ago _ are in operation in the United States, but about 855 R22s are registered in this country.

NTSB investigators have found that ``R22 mechanical reliability problems have not contributed significantly to the accident rate compared to other light utility helicopters, but the R22 has had an unusually high number of accidents attributed to pilot performance or undetermined causes (including in-flight rotor instability and breakup accidents) compared to other helicopters,'' the NTSB said.

An R22 crashed near Zurich, Switzerland, on Dec. 27, killing the pilot and a passenger, the NTSB letter said. On Sept. 28, an R22 being operated by a business crashed near Knightdale, N.C., after the helicopter's tail broke off the helicopter. The pilot died.

An R44 broke apart about 2,000 feet above the ground and crashed near Speyer, Germany, on Dec. 8, killing an experienced flight instructor and a student. And on April 2, a private pilot and his wife died after an R44 crashed near Hanover, Germany.

The helicopters were traveling at moderate speeds in each case, the NTSB said. Investigators found no evidence that the pilots were operating the choppers improperly, the NTSB said.

After a September 1982 crash near Paige, Texas, the NTSB recommended grounding the R22 until a study of its rotor assembly was completed.

Later that year, the FAA decided against doing that after flight tests and a rotor design review. The agency also put out a bulletin emphasizing flight instructor responsibilities during student training.

Last July, the NTSB made a second set of recommendations on the R22, this time asking the FAA to reduce the maximum speeds at which pilots may operate it while officials study the problem.

In response, the FAA convened a panel to research R22 in-flight breakup accidents in October. The FAA decided against restricting R22 flight operations until the panel's work was finished, however.