Major players in the television and film industries are nervously looking to Washington for new government guidance that will help shape the future home video market.

What the television networks and movie studios are awaiting is word from the Justice Department's antitrust division of how it plans to monitor the burgeoning and increasingly complex video world, now undergoing a rash of mergers and joint ventures that are likely to dictate the industry's structure for years to come.

The antitrust division is currently evaluating two major television-film deals.

The first, announced late last year, would establish a new major Hollywood studio involving $400 million in funds from CBS Inc., at present the number one prime-time network; Time Inc.'s Home Box Office, the runaway leader in pay television; and Coca-Cola Co.'s Columbia Pictures.

The second involves the combination of HBO's two principal competitors, Showtime, currently owned by Viacom International Inc., and The Movie Channel, a joint venture of Warner Communications Inc. and American Express Co. Showtime ranks second in pay TV behind HBO, while The Movie Channel is third.

Under the arrangement announced almost two weeks ago, the operators of these two services would join with MCA Inc., parent of Universal Studios; Paramount Pictures Corp., a Gulf and Western Industries Inc. subsidiary; and Warner Communications Inc., the Warner Brothers parent.

Most antitrust observers feel there is little likelihood that the current trustbusting team under antitrust chief William Baxter would challenge the CBS-HBO-Columbia deal, although the department has announced that it is conducting an investigation.

Opponents, particularly studios not participating with CBS and HBO, are beginning to complain that the distribution mechanism that deal creates would give the venture an unfair advantage over competing studios. The new studio could move films from theaters through Columbia's theatrical distribution network to pay television and finally to over-the-air television. In addition, the deal combines three strong sources of financial backing for made-for-television films and other productions.

A more thorough investigation of the Showtime-Movie Channel agreement has also been launched. The government has asked the partners for large amounts of information on the venture.

One source close to the matter puts the chance of government approval of the The Movie Channel-Showtime pact at only 50-50.

That deal unites the second and third players in an industry and would create a combined subscriber base of about 6.3 million compared to more than 11 million for HBO. HBO also has a sister all-film service, Cinemax, which has about 2 million subscribers.

This combination of competitors has raised serious questions within the current antitrust division and surely would not have been cleared by Justice under the Carter administration, observers say. That antitrust division blocked efforts in 1980 by four film companies and Getty Oil to form Premiere, a pay television service different from the current venture in that it specifically called for exclusivity on cable and pay television distribution of the studios' films.

Clearly, these agreements strengthen dominant companies in industries, making it harder for new entrants. In fact, most industry observers think it will be next to impossible for anyone to develop new services as powerful as HBO, an increasingly important funding source for films and television programming, let alone networks with the potential strength of a combined Showtime-Movie Channel.

Furthermore, both Viacom and Warner Bros. operate local cable systems that could exclude services from distribution. Critics also suggest that the studios could set prices for film rights that make their purchase unlikely, limiting access to new matericals in the video market.

However, defining the relevant market in this field for the purposes of antitrust review requires a refined degree of crystal ball gazing. There is little, if any, precedent for evaluating a deal for antitrust purposes based on projected market positions.

The pay cable market, while ballooning to over 20 million of the approximately 30 million homes with cable TV, is still a developing business, and its growth is dependent upon how quickly cable operators can build new systems, particularly in large cities, and how well those pay services can be marketed.

But the best evidence of the importance of the pay market is the fact all three major commercial networks are in the pay television business in one form or another. In fact, executives of American Broadcasting Cos. Inc. seriously considered buying into Showtime to add to their already planned business in sports pay television, though those plans were abandoned.