Democrat Michael Dukakis declared on Friday that "things have been getting a little shrill on the Republican side" and urged rival George Bush to agree to meet him in a series of debates.

A Bush spokeswoman brushed the challenge aside while the vice president welcomed aboard his new campaign chairman, James Baker III, who is resigning as treasury secretary to take the post. Baker's resignation is effective Aug. 17, the day Bush will receive the Republican presidential nomination. (See story on A1.)Meanwhile, a White House doctor released a statement giving particulars of Bush's physical condition and pronouncing him "an unusually active and healthy man."

Also on Friday, a spokesman for Sen. Lloyd Bentsen of Texas said the Democratic vice presidential nominee is resigning from three exclusive clubs, two in Houston and one in Middleburg, Va., outside Washington.

At least two of the clubs do not have black members, but officials of all three said none excludes membership to any group of people. Bentsen "just felt it was the appropriate thing to do," said his spokesman, Jack DeVore.

The manager of one of the clubs, the Ramada Club in Houston, said Bush had been a member until shortly before becoming vice president. The manager described the club's membership as "mixed." A 1980 Houston City magazine article, citing figures from a congressional committee, said the club had no black or female members.

Bentsen was on Capitol Hill, working on Senate business, but was rejoining the campaign trail Saturday with a trip to Corpus Christi, Texas. He was to address the same Hispanic veterans group that heard Bush strongly attack Dukakis' defense policies on Thursday.

Dukakis, campaigning Friday in Laguna Beach, Calif., noted the attack and retorted that Bush "in my judgment doesn't have what it takes to lead this country in foreign policy." He challenged his Republican rival to devote their first proposed debate on Sept. 14 to foreign policy and national security issues.

"I think the American people want a debate on the issues, and I think it's about time we began planning for it," Dukakis said.

Dukakis spoke at a news conference as his campaign released a letter from top Dukakis campaign officials to the Bush campaign asking the vice president to agree to a set of three proposed presidential debates, and a fourth between their running mates. The debates were proposed by a bipartisan presidential commission, beginning with the mid-September debate in Annapolis, Md., and Dukakis said they were generally agreed to earlier this year by all the presidential candidates including Bush.

After his White House appearance, Baker said, "I am a realist about the difficulty of the task that faces us," taking note of Bush's lagging position in the polls. He said Bush has previously overcome similar poll deficits.