Two Northern Virginia men were being held in a jail near Richmond yesterday in lieu of a $150,000 bond after Virginia State Police charged them with conspiring to rob the King's Dominion amusement park at Doswell.

Neither police nor park officials would reveal how the state police learned of the alleged plot, but a King's Dominion spokesman said amusement park officials had been warned by police of a robbery threat.

The two suspects held at the Hanover County jail were identified by police as Sherman W. Phillips, 39, of Falls Church and Robert M. Simms, 31, of Alexandria. Virginia State Police said the two men were arrested Monday in the Northern Virginia area and are scheduled to appear in court in Hanover County today.

"Had the robbery been successful it would pretty much have been a futile attempt . . . because we keep little money here," James E. Copp, the comptroller of King's Dominion, said in a telephone interview yesterday.

Copp said that the money taken in at the park, much of it in cash or travelers checks, is picked up by armored trucks several times a day and taken to a storage vault, Copp refused to say how much money was usually kept on hand at the amusement park or how much the park collects on a normal day.