Major league baseball is planning a pay-cable television network, television sources said yesterday.

According to the Associated Press, the cable network is expected to be in operation by 1990 and will provide games to already existing cable systems.

Jim Spence, senior vice president for ABC sports, told The Washington Post, "We do have a partnership arrangement that's part of the overall deal between us and baseball. The plan is not at the point of fruition. Major league baseball may elect to put together a national pay cable deal.

"If they do, we and NBC would be part of the arrangement. Baseball is not obligated to put it together and I don't think they have any plans in the short term. Over the course of the agreement, it may evolve."

Spence said he thought the development of a pay-cable network was "likely" though not "definite."

Last week, after four months of negotiation, baseball reached a six-year, $1.2 billion deal with NBC and ABC. A spokesman for NBC yesterday said, referring to the proposal, "It's pay (cable). It's part of the overall agreement reached with baseball."

A spokesman for baseball Commissioner Bowie Kuhn said, "We are evaluating the possibility for the distribution of games to our clubs' pay-TV systems."

One network source told the AP, "Baseball is going to be involved in pay-cable within the next six years."

The executive committee of major league baseball will meet next Wednesday. Edward Bennett Williams, owner of the Orioles, said, "Basically the network deal has to be okayed. That's why we are meeting.

"There are a lot of things with the network deal to be worked out. I think it's premature to talk about cable at this time."

The Orioles are currently exploring possibilities for a local cable network.

Between 30-35 million of the 83 million homes with television sets are wired for cable. Though there is no cable television in the District of Columbia or Montgomery County, there are 17,000 subscribers in Alexandria, 24,000 in Arlington and 8,500 in Reston.

Prince George's County is beginning to be wired for its cable system. There is no cable in Baltimore, but some exists in the immediate suburbs.

Though plans for baseball's pay-cable system are sketchy, Spence stressed that it would not "reduce or alter what we do on the network. We're still going to be doing prime-time games and potentially a number of Sunday games . . . Say ABC had a game on a Monday, they would not be opposite us. It would be a night where it wouldn't conflict."

Pay television would be potentially very lucrative for baseball, particularly for the World Series and playoffs.

The new network contract guarantees that they will be telecast on the major networks, in alternating years, through 1989.

Several teams, including the Chicago White Sox, already carry games on pay-cable television. The New York Yankees and New York Mets are both carried on SportsChannel.

The Associated Press said that, according to sources, ABC and NBC would be financially involved in the project. One source said one reason the negotiations on the new contract took so long was the networks' desire to be included in cable revenues.

But AP sources also noted that any operation involving both networks at the same time could run into antitrust problems.

Spence said each of the networks had concluded separate deals with baseball to avoid any antitrust problems.

Another possibility, less likely because of the cost, would be a special channel, like Home Box Office and other subscription movie outlets, in which subscribers would pay extra to see baseball games.

Baseball is currently on cable nationally on the USA network, which is part of basic cable with no extra fee.

One problem the planners face is a market that primarily is local during the regular season. The new network contract permits teams to broadcast locally on cable while a network game is in progress, but bans over-the-air television in that time period.

The reason for the ban, insisted upon by NBC, was evident in the ratings of NBC's first Game of the Week, last Saturday between the Montreal Expos and the Los Angeles Dodgers.

In three major cities, New York, Chicago and Philadelphia, the Game of the Week lost in the ratings by margins of 2-1 and 3-1 to telecasts of the local teams.