A Hyattsville woman yesterday filed a $6 million damage suit against several federal agencies, contending that she was exposed to radiation in 1957 while watching 16 atomic explosions from an observation post 20 miles from a Nevada nuclear testing site.

Ann Mark, who was a typist for the Atomic Energy Commission in 1957 at its Nevada testing site, developed cancer two years ago.

In the lawsuit, she asserts that several federal agencies "intentionally failed to warn" her and others of the risk of radiation exposure and later "concealed" their "negligence"

A spokesman for the Department of Energy, one of the defendants named in the lawsuit, said it is "extremely doubtful" that a person 20 miles from an atomic explosion would be exposed to the "primary" radiation it emits.

David S. Miller, who works at the department's Mercury, Nev., testing site, said that "fallout" radiation would only affect those "downwind" from a blast, and "you just don't put people downwind."

Mark states in the lawsuit, filed in U.S. District Court in Baltimore, that she discovered she had cancer of the cervix in 1977, and that later she suspected a "causal connection" between the disease and her exposure to "ionizing radiation."

She claims in the suit that during "off-work" hours and "break periods" from her job, she was "invited" to watch the explosions along with other employes.

The suit alleges that the DOE, the Department of Labor and the Department of theArmy have violated her constitutional rights to equal protection of the law by ignoring her claims. The agencies also violated the rights of other civilian workers and servicemen who suffered from illnesses that may have been linked to radiation exposure, according to the suit.

Dr. Edward P. Radford, a specialist in environmental medicine at the University of Pittsburgh, agreed yesterday with DOE's assessment that it is "unlikely" that primary radiation would effect a person 20 miles from an explosion.

Radford also said "there is little evidence that there is a risk of cancer of the cervix from radiation."

But Mark asserts in her lawsuit that as early as 1951, the defendants had "medical and scientific data which clearly indicated that ionizing radiation was likely to cause cancer . . . in humans." Despite this, the suit alleges, the defendants acted negligently.