The USS Monitor, the ironclad Civil War vessel that sank in a storm 117 years ago, will be entered for the first time next month when scientists cut an opening in the sunken ship and attempt to remove artifacts from her officers' quarters.

This would be the first full-scale examination of the ship by researchers since it was discovered 20 miles -- and 220 feet deep -- off Cape Hatteras, N.C., in 1973. Scientists on the diving expedition also hope to learn whether the famed Union ship can be raised.

Spokesman for the National Oceanic and Atmospheric Administration yesterday announced plans for the month-long expedition, calling it "the most important underwater archeological event of this century."

The NOAA administrator, Richard Frank, said about 30 divers, scientists and technicians will photograph the wreck from every angle, retrieve artifacts and test the ship's structural soundness.

The Monitor made naval history on March 9, 1862, when it engaged the Confederate ironclad Merrimac in a battle that ended the era of wooden fighting ships. Nine months later, while being towed south for blockade duty, she foundered in a gale and sank with a crew of 16 men.

There have been two ppreviouus expeditions to the wreck site. In 1977, drivers photographed the upside-down ship and retrieved a brass lantern and other small pieces of metal lying nearby.

But those underwater missions were intended to serve as preparation for the one next month, according to NOAA officials. They said no one has actually boarded the ship since its discovery.

"It's pretty crunched up," said Bill Brennan, a NOAA spokesman who described plans for the expedition. "Whether it can be raised or not we will begin to learn from this exploration. We don't know if it will fall apart, particularly if it is exposed to air."

The $265,000 August mission is jointly financed by NOAA, the state of North Carolina and the Harbor Branch Foundation, a private, nonprofit oceanographic research organization based in Pierce, Fla.

NOAA designated the Monitor wreck site a marine sanctuary in 1975 to protect the historic ship from damage by souvenir hunters. CAPTION: Picture, While being towed in 1862, the Union ironclad Monitor foundered in a gale and sank.