Two of the nation's major newspaper powers, Dow Jones & Co and Knight-Ridder Newspaper Inc., have made a $237.6 million joint offer to purchase UA-Columbia Cablevision Inc., the nation's 10th-largest cable system operator.

If the board of UA-Columbia accepts the bid at a meeting next month, the merger would mark the first move by Knight-Ridder into the cable television industry and would represent a significant addition to Dow Jones' fledgine efforts in the cable market.

The proposal calls for the two companies to make a cash purchase for all 3.3 million outstanding shares of UA-Columbia for $72 a share. UA-Columbia had been touted by industry anlyst as a potential takeover target because it is one of the few remaining major independent cable companies.

The cable company, which is based in Westport, Conn., operates systems in 16 states for about 420,000 subscribers. The company's largest system is in the northern New Jersey, although it is building a new cable system for San Antonio, Tex.

UA-Columbia is also a partner with Madison Square Garden in the USA Network, a cable programming network that specializes in sports events and is the fifth-largest of the cable networks.

Robert Rosencrans, president of UA-Columbia, said the proposal would be evaluated by company management. "There is no assurance that the proposal will prove acceptable to the company's board," he said.

In a statement, Knight-Ridder and Dow Jones said they will "jointly and equally" own a new corporation which will be merged with the cable concern. The two news companies said they plan to retain current Ua-Columbia management.

"We have made what we regard as an excellent offer to UACC because we believe this fine company and its first-class management will provide each of us with an excellent entry into cable television," said Alvah H. Chapman Jr., president of Knight-Ridder, and Warren H. Phillips, chairman of Dow Jones.