Round two of the Federal Trade Commission hearings on "kidvid" -- television advertising aimed at children -- opens in Washington today, amid an air of compromise.

While the more than 120 witnesses in five weeks of hearings scheduled here are bound to echo the emotional tone of the first two weeks of hearings in San Francisco in January, there are indications that both sides of the question are seeking a negotiated, informal solution to the argument over if and how companies can use television to advertise to youngsters.

FTC officials have said provately they see little hope for implementation of their staff proposal calling for a total ban on television advertising to children supposedly not old enough to understand the difference berween advertising and programming.

But they quickly add they do hope to make "incremental gains" that would limit the type of advertising presented to children and distinguish advertising from regular programming.

And there are indications both sides are beginning to approach the kidvid proceedings with the same attitude.

Although the issues surrounding the FTC investigation of children's advertising are much broader than just the effects of ads on children -- constitutional questions of free speech for advertisers, the role of government in usurping parental decisions, the statutory limitations of the FTC, to name a few -- both sides now appear to be gravitating toward the central issue: Can and should television be used to advertise to young children?

"In the past hearings" said Choate, president of a nonprofit consumer group, the Council on Children, Media and Merchandising, "testimony on advertising seen by children has been presented only in black and white -- either in terms of complete satisfaction with the status quo, or, the exact opposite -- that the only solution is a total ban."

But Choate will make a compromise proposal when he testifies before FTC administrative law Judge Morton Needelman in Washington a week from now, a proposal he says "advocates a pragmatic, middle position. It does not infringe on First Amendment rights cited often by the business community; at the same time it recognizes the special vulnerabilities of children as they watch television commercials."

Specifically, Choate is calling for devices that would separate advertising from regular broadcasting on television.

He wants both an announcement and a "frame-like device" to be used to separate advertising and make it look distinctly different on the screen. A border around the outer edge of the screen, for example, could serve to make advertising noticeably different, even when seen only in a glance.

Choate also wants advertisers to reveal the approximate maximum cost of any product being hyped that is worth more than $2, advisory messages in white on black with audio repetition, a nutrition-related graphic symbol to portray relative nutritional worth of the product, indications of product hazards for child usage, and a required advertiser-funded public service message on nutritiondental health in each broadcast half hour in which four or more edible product commercials appear.

And, unlike previous proposals that are limited to Saturday mornings, when children's programing is in abundance, Choate wants his rules to deal with all television programing before 9:30 p.m., "when children represent a (large) percentage of the audience."

On the industry side of the question, the American Broadcasting Co. announced druing the San Francisco hearings that it would cut back advertising during children's programing on the ABC-TV network by 20 percent, in two stages, between now and 1980.

Then, after the hearings ended, the same network called for "separators" between children's advertising and programing. Although all three major TV networks have used some form of separator -- usually lasting between three and 12 seconds -- since 1975, whem the National Association of Broadcasters called for such a practice, ABC is calling for standardization of such messages.