It was a classic showdown.

Liberty versus authority. Kids versus grown-ups. Green versus Blue.

And at halftime of Harvard's 17-7 victory over Dartmouth Saturday, the confrontation began.

Hundreds of Little Green freshmen, following an old Dartmouth tradition, wanted to run onto the Stadium turf and form their class numerals.

Half a dozen Harvard University policemen wanted to stop them.

And it wasn't pretty.

"We didn't have anywhere near enough people to control it," said University Police Chief Paul E. Johnson yesterday. "It was completely unexpected."

Johnson, pleading ignorance of Ivy League tradition, said he wasn't prepared for the bi-annual Dartmouth 'shmen ritual. "I had no information on any of that," he said.

The Men (and Women) of Dartmouth traditionally require their freshmen to stand during football contests, and to perform a ritualistic halftime dance. It is a custom born in a northern land where there's nothing better to do.

Johnson, sensing the spirit of the Big Green crowd, said he massed his men in front of the freshman section "to see what hijinks they were up to."

"We were prepared for any capers," he added.

Well, almost any capers. The University's finest weren't ready to stop hundreds of Dartmouth 'shmen from swarming onto the turf like so many green-clad cockroaches.

The freshmen were warned by the Dartmouth administration last week that Harvard cops might not be the Officer Friendlies that patrol Hanover. Nevertheless, the resourceful 'shmen had little difficulty flaunting the long arms of the law.

At first, the Men in Blue tried to physically block the Kids in Green from taking the field. But the five or six cops were no match for an entire Dartmouth class.

After wrapping a few of the 'shmen in bear hugs, and striking one ("I didn't see that," Johnson said), the policemen decided to give up and let the freshmen do their thing.