Readers of The Washington Post may have noticed that some sections of the paper have taken on a slightly different appearance over the past few weeks.

The reason is simple: The Post is in the process of changing the way in which stories are written and type is set. The conversion is from metal type (in which each line is set on a linotype machine) to what is known as cold type (in which pictures or photographs are made of each line of type.)

What is happening is that reporters and editors are being provided more modern tools with which to record their stories. In the past, the process utilized paper and typewriters. Now it is done with electrons.

Nothing is simple after that has been said. The new process is sophisticated and complex. It will change forever how reporters record their stories, how editors edit the stories, how headlines are composed, picture captions writen, corrections made and all the other hundreds of jobs that go into assembling a modern newspaper each day.

As readers may have guessed by now, the heart of the new system is a computer. Reporters and editors now work in front of video display terminals (VDT's for short). The terminals look like television screens and have a more elaborate keyboard than typewriters, including keys that insert words, delete them, give them bold face characteristics and italics. The keyboard also includes a key mark "help."

Any new computerized system goes through a "shakedown" or "debugging" period.In simplier times, this was known as Murphy's law: Everything that can go wrong, will. The Washington Post's new system is no exception.

To ease the transition, The Post is changing over to the new system one section at a time. The Sports department made the change Sept. 1, the Metro department with today's paper. Several other departments have been on a smaller, interim system for several months.

In about a month, all sections will be on the new system and there no longer will be any discrepancies in the way the paper looks from one section to another. At that point, the entire paper then will use a typeface called Century Schoolbook. The size of the type will be 10 points. To see what that type looks like and how big it is, look at today's Washington Business section or the Friday Weekend section. Both now are printed in 10 point Century Schoolbook.

One of the problems during the transition period has been that some stories have not made all editions of the paper, and some corrections to stories were not made in time. Again, these lapses are as inevitable as they are temporary.

When the new system is completely in place, The Post believes it will have the largest, most modern and complete VDT system in use at any newspaper in the country.

The system was jointly designed by The Post and the Raytheon Company. After a contract was signed on Aug. 18, 1977, it was built by Raytheon's Equipment Division in Sudbury, Mass. The contract price for the system was $5,250,000.

Unlike some other metropolitan newspapers, which have combined a number of smaller systems to accommodate a large staff, The Post will have 292 VDTs, and all reporters and editors will have access to stories at a moment's notice. The system can accommodate 64,000 stories -- roughly 30 million words -- and all of them are stored in one location, called a "central data base."

Terminals also will be located outside of the The Post's main office -- bureaus staffed by Post reporters in the Washington suburbs as well as places such as Richmond, Annapolis and Los Angeles. In addition, reporters also will be able to take portable terminals with them when they travel out of town.

Considerable effort has been made to ensure security, ranging from individual, secert passwords that are used when a person begins work each day on his terminal; restrictions to ensure that only certain people can typeset or make changes in stories; and the equivalent of a "locked desk drawer" for individual users.

Stories move through the system in an organized way.When a reporter tells the computer that he has finished writing a story, it automatically is sent to the reporter's editor. The editors make the changes they wish while the story is on their screen. The system keeps track of those changes -- in fact, of any changes made to a story during its journey into the paper -- and this "edit trail" can be retrieved for checking. It can thus be determined who made what changes in a story from the time it was first assigned until it is published.

Editors also write headlines for stories on the screen and add commands that act as instructions to the phototypesetting machine. Those instructions include such things as the size of the headline and whether it is boldface or italic, the width of the headline, the size of the type in the story, the width of the columns, and the length of each column of type. If the headline the editor writes is too long, the computer will say so and tell how long it is. The same things happens if the headline is too short.

When the editor is finished, he presses a button labeled Typeset," and the story is sent to the phototypesetting machine. The story goes in exactly as it will appear in the paper and comes out the same way. It emerges on paper film, which then is pasted onto cardboard pages. Once the page is completed, it moves to the next step of the production process.

Beginning next month, the pasted-up pages will be scanned by a laser device and images of them sent by microwave to The Post's new printing plant in Springfield. Once there, the images will be converted to plates for the three new high-speed presses being installed there. The Post thus will be able to increase the number of papers it can produce every day.