Vice President Al Gore said today that the White House should release a modest amount of oil from government stockpiles to try to stabilize oil prices, a move that Gov. George W. Bush immediately denounced as a political ploy that could endanger national security.If Mr. Clinton acts on Mr. Gore's proposal to release at least five million barrels of oil - about what the United States consumes every six to nine hours - it would be the first time the reserve had been tapped since the Persian Gulf war.