Just touch this computer's screen and it performs

Everyone can point, but many people can't type. This observation underlies the design of a new desktop computer. Just announced by Hewlett-Packard, this computer has a price tag and capabilities very similar to IBM's best-selling Personal Computer. But it has a major distinction: a touch-sensitive screen.

This allows users to operate the computer by simply touching a finger or pencil to designated spots on the screen. Besides serving as a clever gimmick to differentiate the HP-150 from its competitors, the touch screen is the latest attempt by manufacturers to outflank the typewriter keyboard, which many see as a major stumbling block to the spread of small computers. It is also a manifestation of the continuing effort to produce machines that are easier to use. This is considered essential if computers are to fulfill their revolutionary promise.

Just how this latest device works was illustrated at the unveiling of the new computer last week. One of the most graphic examples is a filing program:

Etched on the glowing computer screen is a line drawing of an address file, depicted as a series of tabbed cards. Hold a finger on an illuminated square at one side of the screen, and the ''cards'' begin scrolling downward, like turning a rotary index file. Remove the finger, and the cards stop moving. All it takes is a touch on one of the tabs to ''pull'' and display a card, complete with name , address, and telephone number. Another touch, to a square at the bottom of the screen, and the computer automatically dials the phone number listed on the card.

''We believe that the touch screen will set a new standard for ease of use, and more important, ease of learning,'' summarized James E. Carlson, marketing manager for HP's Personal Office Computer Division.

Marketing surveys have found that many business people - the primary purchasers of this type of computer - are poor typists and further consider it beneath their dignity. This has limited the personal computer's usefulness and appeal in the office. A recent Yankee Group survey of business executives found 50 percent of those with computers used them for less than 30 minutes a day and were dissatisfied with them.

Thus, Apple's Lisa, introduced earlier this year, features a device dubbed the ''mouse.'' This is a small box that fits in the palm of the hand and is connected to the computer by a slender cord. Sliding it around on a tabletop moves the computer's pointer, or cursor, around the screen. With the mouse, the user selects from a menu by placing the cursor at the designated position on the screen and pushing a button on the gadget's back.

Texas Instruments' approach to this problem has been quite different and reflects its background in computer voice synthesis and recognition. It has given its ''Professional'' model the ability to recognize up to 200 spoken commands. The operator simply speaks key words into a microphone and the computer responds as if they had been typed on the keyboard.

Like the mouse and voice recognition, the touch screen has been employed on larger, special-purpose computer systems for some time. It uses a series of narrow light beams crisscrossing just in front of the screen. Touching the screen breaks some of these beams, allowing the computer to determine the finger's location. But this is the first time a touch screen has been fully integrated into a general-purpose microcomputer.

The introduction of these devices also reflects an awareness among computermakers that their products are still too complicated for many people, despite advertising campaigns that all too often make their use sound simple. Programs for word processing, filing, and financial planning typically require the memorization of dozens, even hundreds, of commands.

The primary thrust to circumvent this problem has been the liberal application of menus. To operate a program, the user is presented with a series of choices. In complex software, the operator must often go through a number of menus to perform a given action. While using menus is much simpler than memorizing commands, it does have a drawback: It can be extremely time-consuming.

The Lisa and the HP-150 represent refinements to this basic approach. The Lisa uses small symbols instead of a written menu. For example, a picture of a trashcan stands for deletion. The basic idea is that these are easier to remember than key sequences. And because they take up less space than written descriptions, more can be placed on the screen at a given time.

Hewlett-Packard's solution is less sophisticated than Apple's. Its screen does not have the high resolution of the Lisa, which is required for the use of small symbols. As a result, it is generally limited to half a dozen selections at a time. While pointing may be faster and more natural than finding the right key for many people, having to wade through a number of menus by touch can be nearly as time-consuming as doing so using a keyboard.

On the other hand, the price of the HP-150 is substantially less than that of Lisa. It starts at less than $4,000, while the Apple computer is listed at $10, 000. (Slow sales have caused Apple to reduce Lisa's price by as much as $3,000.) Also, Hewlett-Packard's machine will run a large number of the popular programs that have been written for the IBM personal computer, whereas the Lisa is limited to programs written specifically for it.

While the touch screen has some limitations, it also has some intriguing possibilities. For instance, Hewlett-Packard is developing a program that will mimic one of its popular financial calculators. A drawing of the calculator will appear on the screen and it will be operated just like the real thing, by pushing its ''buttons.''