IF YOU FIND that the heat of the Mall is getting you down on this holiday weekend, you might want to stop by the National Archives on Pennsylvania Avenue. There in its cool halls you can take a walk through the early history of this nation. The original copies of the Declaration of Independence, the Constitution and the Bill of Rights are on display along with a special exhibit of other documents from the period when the Union was formed.

If you come back on a working day, the Archives staff will help you gain access to a truly marvelous collection of government documents, films and tapes that record the workings of the federal government right up to the present day. You can even see Eva Braun cavorting on Hitler's lawn in a captured World War II film, look up your ancestors in census files going back to 1790 or listen to Richard Nixon discussing Watergate with his staff.

What you won't see is the behind-the-scenes struggle of the Archives' skilled staff to keep up with the ever larger burden of cataloging and maintaining current additions to its holdings while trying to preserve historical acquisitions from deterioration. The Archives' difficulties are not new, although they have worsened in recent years. A sharp budget cut in 1982 cost the agency 20 percent of its staff. Congress restored some money last year and will probably resist administration proposals for further cuts. But skilled archivists have fled to more congenial institutions, and the agency's resources remain woefully inadequate to its responsibilities.

The Archives' long history of neglect dates back to the 1950s, when it lost its status as an independent agency and was put under the control of the General Services Administration, the federal government's scandal-prone housekeeping agency. Without independent access to either OMB or Congress, the Archives has not been able to make its case for the specialized resources and attention that it needs. While the independent Smithsonian and Library of Congress have flourished, the Archives has beome the stepchild of the nation's historical and cultural institutions.

The current GSA administrator, Gerald Carmen, has made substantial progress in improving that enterprise, and he commissioned an internal study to look into the Archives' special problems. But GSA is a huge agency, and its mainline interests and methods of operation are necessarily very different from those of the Archives. The obvious solution-- recommended by numerous studies and strongly supported by historical and archival associations-- is to make the Archives an independent agency.

Sens. Charles Mathias and Thomas Eagleton recently reintroduced legislation to give the Archives independence. Administrator Carmen has not yet decided what action to take, but the study he commissioned recently recommended steps giving the Archives significant autonomy, although not the independent administrative and financial control that it needs. Even though the move need not add to administrative costs, the Reagan administration will naturally be reluctant to add another box to the government's organizational chart. But that would be an insignificant price to pay for ensuring that the Archives' national treasures are carefully preserved.