IBM Corp. is expected to announce this week that it will begin marketing office telephones and personal computers as a package through its newly acquired Rolm Corp. subsidiary.

The new computer phones would be IBM's first voice communications product in this country and would represent the computer giant's boldest challenge yet to AT&T's dominance of the office communications marketplace.

This mix of the two technologies highlights what most industry experts believe to be the ultimate convergence of the telecommunications and data-processing industries.

IBM announced earlier this month that it intended to acquire Rolm, a Santa Clara, Calif.-based manufacturer of office telecommunications switching equipment, for $1.25 billion. This marked the first time IBM had purchased a company outright since 1962.

The new office work station, called Cedar, blends IBM's popular personal computer and a telephone into a single desk-top package. Cedar links into Rolm's line of PBXs, which is the central switching technology that currently links telephones.

With more than $650 million a year in revenue and more than 15,000 corporate customers, Rolm is a leader in the $3 billion office PBX market, competing against AT&T and Northern Telecom.

With Cedar, which has been under development at Rolm for more than a year, a user would be able to send voice and data communications through the phone lines simultaneously. The unit offers a high-resolution, 80-by-25-character screen, high-speed data communications ability, a multiline personal phone, a speakerphone, a built-in calculator and 512 kilobytes of memory.

The so-called "integrated work station" offers one-touch "log-on" to tap various data bases and retrieve phone numbers from the computer phone's directory. The computer comes with dual disc drives and unspecified "productivity software." Software also enables it to emulate several different kinds of computer terminals.

Shipments of Cedar are expected to begin early next year.

The package is expected to cost more than $4,200, which two analysts, who asked not be named, described as "very aggressive."

They point out that Cedar, when linked to a Rolm PBX, immediately would offer offices a local area network over which voice and data communications could be exchanged easily. Many experts believe that linking personal computers and large computers into networks creates electronic-mail and other opportunities that will improve white-collar office productivity.

There are a variety of local area network approaches, but some only link computers and exclude voice. The fact that the PBX can carry both voice and data makes it an appealing choice for building a local corporate communications network.

The announcement also is expected to include the introduction of Juniper, a telephone attachment to the IBM Personal Computer that gives it Cedar-like capabilities. The Juniper adapter board is expected to sell for roughly $1,500.

Other companies are exploring the integrated telephone/computer work station. Compaq Computer Corp., which manufactures an IBM-compatible computer, reportedly is developing a computer phone. So is Zaison Inc. of Houston.

AT&T does not now offer a combined computer/phone package.