Doctors here have had "encouraging" results treating two stubborn kinds of cancer by exposing patients to the powerful neutron beam of a Naval Research Laboratory atom smashing machine.

The unconventional treatment of cancer of the stomach and the pancreas was conducted by a team from Georgetown and George Washington universities at the $7 million facility built by the Navy to investigate the atom.

Naval Research Laboratory physicists use the stream of neutrons or atomic particles created by the 32-foot-long machine, located on the Potomac River to penetrate and break up atoms.

Starting in 1973, a consortium of 20 mid-Atlantic region universities began sending cancer patients to Washington to see if the same kind of atomic particles would break up cancer cells.

"We've been reading a lot about neutron bombs that would use neutrons to cause damage," one project doctor commented yesterday. "Here's a case where neutrons may damage cells, but - if the treatment works out - the result may help our patients."

The George Washington George town team - Drs. John McDonald, Lawrence Hill, Philip Schien, Paul Wooley III, Charles Rogers and Robert Ornitz - treated seven patients with gastric or stomach cancers and 13 with pancreatic cancers beginning in 1975. Each was treated for nearly six weeks with neutron beam and received as well several doses of the chemical five-fleurouracil, know as 5FU.

Of the seven patients with gastric cancer, only one is still alive. But there was no visible cancer at all when the survivor, a woman in her late 50s, had to be operated on for another reason sometime after her treatment.

Of the 13 patients with pancreatic cancers, three are alive. The treatment shrank the tumor in these three patients and two others by more than 50 percent.

"We aren't claiming any cures," said Dr. Wooley, a member of Georgetown's oncology or cancer treatment unit. "We do have a few survivals in these categories of cancer that have had a partially dismal outlook. And we have seen some shrinkage of tumor that we wouldn't have expected with other treatment.

"What we do say is that we now believe this treatment is worth much more investigation, and there should be a large-scale, controled national trial comparing results of this therapy with other treatments."

An enlarged trial was started Wednesday, said Dr. Ornitz, one of two George Washington University radiation oncologists who direct the neutron-beam treatments at the naval laboratory.

There have also been some "very encouraging" response in patients with head and neck cancers (specifically, squamous cell carcinomas), Qrnitz disclosed.

Again, these have only been pilot studies, he said. "We must move to larger-scale comparisons with other combinations of treatment before we can say more," he said.

Both pancreatic and gastric cancers are normally treated either with radiation from less powerful sources or with chemicals or both. For both, the radiation is usually delivered by either a radioactive cobalt source or a linear accelerator, another type of atom-smasher.

But many cells in the centers of large tumors are protected from the rays of these sources because they do not possess enough oxygen, which plays a role in the ways the rays act.

"Since the ability of fast neutrons to kill cells does not require enhancement from oxygen," McDonald said, "fast neutron therapy may result in increased tumor cel deaths.

"I think the track record for the last 20 years," he said, has been one of trying "various modalities in various combinations" until "in some kinds of cancers, this has let to better treatment."