Doctors don't usually do it, and neither do engineers. But more and more journalists are going into court as expert witnesses -- in effect, armchair quarterbacks who second-guess the professional performance of their colleagues.

The market for expert witnesses in libel cases has been booming -- in part, many feel, because of the 1974 Gertz v. Welch case, which effectively made news organizations more vulnerable to suits and therefore increased the need for witnesses expert in the news field.

The cause of the boom is being debated. Some say that the number of libel suits has increased nationwide. Others see an increase only in the number of suits going to trial. All agree, however, that lawyers are making greater use of expert witnesses to buttress their claims that news organizations are negligent.

Among the experts is Philip Robbins, dean of the two-member journalism department at George Washington University and a former assistant city editor at the Washington Star.

Robbins testified earlier this month on behalf of a Florida businessman who took exception to an investigative report in The Tampa Tribune that accused him of deceptive advertising and illegal business practices. The story was false, the businessman asserted, and no one at the paper had called to ask him to refute the accusations point by point.

Robbins explained to the jury what standards reporters and editors are expected to follow, standards which in this case apparently had been ignored. He said The Tribune had an obligation to be through and accurate, and in this case it was negligent. Proving negligence can be fundamental to winning any libel case.

In this case, the jury found the Tribune negligent to the tune of $630,000 in damages, which the judge later reduced to $380,000.

Robbins said he had "no qualms" about testifying against his former brothers in the profession and would have no trouble doing so again.

Doctors are often criticized for closing ranks and refusing to decry improprieties by colleagues, he argued, and journalists should not expose themselves to the same kind of criticism.

Robbins said he has been asked to testify in local libel cases but has refused. He doesn't want to get involved in disputes with friends, and many Washington area journalists are part-time instructors in his department.

Such a potential conflict involved Robbins in the Florida case. Two Washington lawyers, John Ferguson and Michael Deese, represented the Florida businessman and said they couldn't find any Florida professors willing to testify against the Tribune.

Neither Robbins nor the lawyers would say what the expert was paid for the 40 hours he worked on the case; $50 to $100 an hour would be par for the course.