Transportation Secretary Elizabeth Hanford Dole yesterday announced that three major airlines that provide computer reservation systems to travel agents have agreed to eliminate bias in their favor from those systems.

The three airlines are American, Trans World and United. American and United, the nation's two largest carriers, provide the computer reservation systems for about 80 percent of computerized travel agencies. Eastern and Delta airlines also sell computer systems and are expected to join the voluntary agreement, according to aviation sources.

Trans World's biased screen will be removed immediately; United and American will remove theirs on April 7.

Dole's announcement came a week after Sen. Nancy Landon Kassebaum (R-Kan.) held hearings in the Senate Commerce Committee's aviation subcommittee exploring a possible requirement that airlines divest themselves of the systems.

A regulation adopted by the now-defunct Civil Aeronautics Board forbids bias in the so-called first-screen display a travel agent calls up. However, the airlines quickly developed secondary displays that were biased, then added a feature so travel agents could choose to eliminate the primary display.

It is the secondary bias that Dole's voluntary agreement addresses. The agreement also reflects a somewhat different attitude toward the issue than was taken by Dole's department last week, when Assistant Secretary Matthew V. Scocozza said that, further actions should not be taken until the department "carefully evaluate s the current rule, especially the secondary bias and pricing issues."

Scocozza said yesterday that the new agreement addresses "the most sensitive, emotional issue" raised at the hearing. With that out of the way, I think we have an opportunity to look at all of the computer-reservation-system issues to see if anything appropriate for rulemaking is out there," he said.

Some carriers have charged that even the supposedly unbiased first screen has a bias.