The Commerce Department is expected to issue rules Monday to tighten restrictions on the export of high-level computer software while easing controls on the shipment of less-sophisticated personal computers to such countries as the Soviet Union.

The rules are expected to go into effect early in January.

The regulations are designed to make it more difficult for Soviet bloc countries to secure sophisticated computer programs from the United States and its allies that could be put to military use. At the same time, the rules will ease the way for companies such as Apple Computers and IBM to sell their less-sophisticated personal computers to the Soviet Union, its allies and China.

The loosening of export restrictions could lay the groundwork for a multibillion-dollar market for American, Japanese and Western European personal computer companies.

The effective decontrol of simpler personal computers, such as the Commodore 64, the Apple IIe and the Radio Shack Model 100, represents a recognition by the West that these machines no longer are "state of the art" and would not pose a military threat if they were in Soviet hands. The export restrictions will focus on preventing diversion of such higher-level computers as Apple's Macintosh and the IBM PC-AT.

The imposition of new Commerce Department regulations on high-technology exports reflects agreements by the 15-nation coordinating committee on strategic exports known as Cocom, which governs sales of all sensitive technology to Warsaw Pact countries.

Cocom, whose membership includes the NATO allies and Japan, meets every four years in Paris to establish a list of "critical technologies" which merit special controls. Cocom is to make sure that member countries have a single policy on which technologies should be withheld from the Soviet bloc and China.

Computer technology is a particularly sensitive subject because hardware (the machines) and software (the instructions that run them) easily can be put to military as well as commercial use.

For the first time, Cocom will require that it review sophisticated computer programs before export by member countries. Such software would include programs that link computers together; higher-level computer programming languages such as Ada, a language used by the Defense Department; computer-aided design and manufacturing software; and artificial-intelligence programs that use software techniques to mimic human reasoning.

Donald Weadon, who represents several high technology companies on export matters, said the rules will assert that "all nonpublic-domain software will be subject to export controls" and that the controls will range from a strict Cocom review to less restrictive "letters of assurance" for the Commerce Department that the software will not be diverted to Soviet bloc nations or China after shipment.

"These rules are a clear implementation at Cocom of . . . a mandate to establish a way to identify and control 'arrays of knowledge' related to computer software," Weadon said.

The Pentagon has been concerned about stemming the flow of technical information to the Warsaw Pact countries. It has asked technical societies in the United States to bar foreigners from attending some meetings.

However, Steven Bryen, deputy assistant secretary of defense for international security policy, said enforcing the new software export restrictions will be "problematic -- everybody knows that" because software can be copied and physically transported or transmitted over international phone lines in the form of electrical impulses.

The Soviet Union is widely perceived as a backwater of computer hardware and software technology. The Soviet government discourages the dissemination of information technologies such as copying machines and telephones.