Chief Justice Warren E. Burger, apparently convinced that ordinary jurors are unable to deal with long and complex civil cases, yesterday urged federal and state courts to study alternatives to jury trials in those cases.

"It borders on cruelty to draft people to sit for long period trying to cope with issues largely beyond their grasp," Burger told the Conference of State Chief "Justices in Flagstaff, Ariz.

"Experienced business and professional people, accountants, professors of economics, statisticians or others competent to cope with complex economic or scientific questions" are often taken off juries by lawyers or excused from service by the court, Burger said.

As civil cases become more complicated, Burger said, trials "last not merely two weeks or one month, but two, six, eight months and even longer."

There follows "an enormous -- inordinate -- impact on the life of each of 12 to 15 lay jurors thrust for weeks and months into a totally strange environment and confronted with the burden of decisions in areas in which they have no experience," Burger said in a speech prepared for the conference.

The day may come, Burger warned, whenn a plumber or an electrician who "customarily earns at least $100 a day" will claim that his constitutional rights are violated when he is compelled to serve on a jury for five or six months at $30 a day.

In "one of those fictions we lawyers love", jurors are presumed to understand instructions on the law given by a judge before deliberations begin, Burger said. But it may take hours and even days for a judge to instruct a jury after a protracted civil case, Burger told the justices.

And, he said, "there is a limit to the capacity of any of us -- jurors or even a judge -- to understand and remember complicated transactions described in a long trial."

Burger proposed that the federal and state courts "inquire into the possibility of some alternatives to jury trial for the protracted trials of issues which baffle all but the rarest of jurors."

In the meantime, he said, "innovative lawyers" could agree to a trial by judge instead of by jury in cases expected to last more than a month. For those who may be "uneasy" about whether a particular judge "is sophisticated in complex economic, business or environmental cases," Burger said the case could be heard by a panel of three judges.