THE CONSTITUTION is edging up to its 200th birthday and doing quite well, especially when you consider the normal life expectancy of such a document. But you wouldn't know it from what happened last week on Capitol Hill. Within 36 hours of the 97th Congress' convening, its members had dropped 66 -- count 'em, 66 -- proposed constitutional amendments into the hopper.

To be sure, there were duplications. Thirty of the 66 dealt in one way or another with budget balancing. These proposals ranged from amendments requiring that appropriations not exceed revenues except in time of war or national emergency to amendments limiting appropriations to 15 percent of the gross national product, whatever that is at a given time.

But enough other amendments were introduced to turn this Congress into a national seminar on elementary civics if its members are so inclined. There were, of course, the hardy perennials: to eliminate the electoral college, to outlaw abortion and to authorize praying in public buildings. But there were others too. For example:

To abolish federal income, estate and gift taxes.

To limit to 18 years the time a member of Congress may serve.

To create a national initiative and referendum system.

To provide representation in the House for the District of Columbia and other federal territories.

To give the president and vice president one six-year term each.

To require Congress to review every rule and regulation promulgated by administrative agencies.

To prohibit anyone from compelling any child to attend any school other than the one closest to home.

It is unlikely that many of this year's proposals will make it into the Constitution. In its first 192 years, Congress approved only 33 amendments, and of those the states have ratified only 26. But there is enough agitation here to suggest the area's scholars might explore before the Constitution anniversary in 1988 how well an 18th-century document serves a 20th-century nation.