Michael Dukakis challenged Republican rival George Bush to spell out his health insurance program for American workers while negotiators for the two candidates wrangled over panel members and lectern heights for the upcoming presidential debate.

One issue, at least, appeared settled Wednesday when a Bush campaign source, speaking on condition of anonymity, said it was agreed that Bush would stand behind a 48-inch-high lectern after his negotiators insisted he would stoop no lower than a 46-inch one. Dukakis, who is five inches shorter than Bush, will stand at a 41-inch lectern.Meanwhile, Dukakis' running mate, Sen. Lloyd Bentsen announced a program to improve rural health care, saying, "Millions of Americans in rural areas are being denied one of the basic necessities of life: They are losing their access to quality health care."

Bentsen, in an appearance Wednesday in Hale City, Texas, said that if elected he and Dukakis would work for the plan including a "hardship fund" to subsidize rural hospitals that are threatened with closure and expansion of a national program providing incentives for doctors and nurses to work in rural areas.

President Reagan, asked at the White House Wednesday whether he'd given Bush any hints about the debate: "Take no prisoners," Reagan responded.

Bush's own political fortunes received a boost from the latest ABC News-Washington Post poll. The survey of 1,271 likely voters found that 70 percent consider the GOP nominee to be a known quantity compared with 54 percent who said they didn't know enough about Dukakis.

The poll, conducted Wednesday through Monday, also found the two candidates in a near dead heat with Bush leading Dukakis 50 percent to 46 percent. The margin of error of three points either way virtually negated the lead. A similar ABC-Post poll released last week found Dukakis holding a slim three-point lead.

Bush was taking the day off to prepare for Sunday's debate with Dukakis in Winston-Salem, N.C. _ the first face-to-face encounter between the two contenders.

While the debate over the debate continued, Dukakis used campaign appearances in Bowling Green, Ky., and Houston to propose a broad health care plan beginning with the 22 million Americans who have no insurance. That would leave 15 million or more Americans still awaiting protection, campaign aides said.

"The simplest and fairest and the most affordable first step toward that goal is to require all employers, with some exceptions for small businesses, to provide basic health insurance for their workers and dependents," Dukakis said.

The plan, similar to one Dukakis signed into law in Massachusetts less than six months ago, would not cost the federal government anything, he said. Dukakis did not provide figures on the cost to employers.

Bush campaign spokesman Mark Goodin branded the Dukakis proposal "socialized medicine" and said, "such is a prescription for financial disaster. The Dukakis plan would put the American economy in the hospital and would list it in critical condition."

Bush's running mate, Dan Quayle, was flying to Arizona to visit an award-winning elementary school before travelling to the California cities of Fresno, Bakersfield and Los Angeles.

Quayle's Democratic counterpart, Bentsen, told voters in Oklahoma that a Dukakis administration would use tax incentives and other subsidies to revive oil production in the Southwest.

He also said Dukakis will "light a fire" under federal regulators blocking the sale of natural gas to the Northeast.