Prominent Democrats yesterday accused President Bush of lying about his military record, even as questions arose about the authenticity of newly disclosed memoranda suggesting Mr. Bush shirked some duties during his stint as a fighter pilot in the National Guard.

“This is about George Bush not doing his duty in the National Guard and then lying to the American people about it,” Senator Harkin of Iowa said at a Washington press conference organized by the Democratic National Committee. “If the president will lie about this, will he lie about how we got into Iraq, for example?”

The attack on Mr. Bush’s honesty followed the disclosure of several purported National Guard memoranda that suggest he may have pulled strings to avoid Guard duties in 1972 and 1973. The documents, featured Wednesday in a “60 Minutes” broadcast, also indicate that Mr. Bush’s superiors were pressured to overlook his absence and his failure to take a physical as ordered.

White House officials dismissed the allegations as warmed-over and said they were the product of desperation on the part of the Democratic presidential nominee, Senator Kerry of Massachusetts.

“These are the same old, recycled attacks that we see every time the president is up for election. It’s not surprising that you see a coordinated effort by Democrats to attack the president when Senator Kerry is falling behind in the polls,” said the White House press secretary, Scott McClellan.

An ABC News/Washington Post poll released last night showed Mr. Bush with 52% support and Mr. Kerry with 43% among likely voters. Among registered voters, Mr. Bush held a narrower 6% lead.

The memoranda in question were apparently written by Mr. Bush’s commander at the 111th Fighter Interceptor Squadron in Houston, Lieutenant Colonel Jerry Killian. Two of the documents bear Killian’s name and signature, while two others are labeled simply, “Memo to File.”

In a May 1972 memo about Mr. Bush’s request to leave the unit to work on a Senate campaign in Alabama, Killian wrote, “He has this campaign to do and other things that will follow and may not have the time. I advised him of our investment in him and his commitment. I… think he’s also talking to someone upstairs.” In August of that year, Killian suspended Mr. Bush from flight status, writing, “Officer has made no attempt to meet his training certification or flight physical.”

Mr. Bush’s allies have argued that his disqualification as a pilot made little difference because the fighter jet he trained on was being phased out. However, Colonel Killian referred to the pilot slot Mr. Bush occupied as a “critical billet.” A few weeks later, in a memo about Mr. Bush entitled “CYA,” Killian apparently wrote, “I’m having trouble running interference and doing my job…I’ll backdate but won’t rate.” Killian died in 1984.

Mr. Bush has denied that he got special treatment in the Guard. However, the president’s aides declined to repeat that assertion yesterday.

While the White House has not challenged the authenticity of the documents, two forensic experts who specialize in detecting forgeries said yesterday they are suspicious of the alleged memoranda.

“They’re very strange documents,” said one leading analyst, William Flynn of Phoenix. He said in the early 1970s there were few typewriting or word-processing systems that allowed both for proportional spacing and the use of superscript, which is seen in one memo. “Taken as a whole, it just doesn’t add up to a document that would have been produced using 1972,1973 technology,” Mr. Flynn said.

Another typewriting expert, Peter Tytell of Manhattan, agreed that those features rarely appeared in that combination at that time.

“I would certainly be curious, if I were you,” he told a reporter.

A third forensic specialist, Dennis Ryan of Merrick, saw no red flags. “Nothing jumps out to me that says this document has been fabricated recently,” he said.

CBS issued a statement yesterday saying it remains confident that the documents are genuine. “Each of the documents broadcast on ’60 Minutes’ was thoroughly investigated by independent experts and we are convinced of their authenticity,” said a spokeswoman for the network, Kelli Edwards. She declined to identify the experts it consulted. Ms. Edwards also said “close associates” of Killian told CBS they saw the memos at the time they were written.

While Mr. Bush’s credibility was under sharp attack yesterday from Mr. Harkin and others, Mr. Kerry stepped gingerly around the issue of Mr. Bush’s National Guard service. During a voter forum in Iowa, Mr. Kerry quickly moved to other subjects after a member of the audience suggested Mr. Bush had difficulty remembering details of his military service.

Mr. Kerry pointed to new statistics showing that health-insurance premiums have increased by more than 50% since Mr. Bush took office.

“We’ve got a health-care system that is imploding on itself,” Mr. Kerry said. “President Bush for four years has had an opportunity to try to deal with this, and he has no plan at all.”

During a speech in Pennsylvania, Mr. Bush ignored the controversy over his military service. He warned that Mr. Kerry planned to increase taxes on entrepreneurs and small-business owners.

“It doesn’t make sense to tax the job creators,” Mr. Bush said.

It remains unclear how voters, particularly undecided voters, will respond to the renewed focus on events of more than three decades ago. However, a backlash of sorts appears to be developing among some in the press.

An anchor for CNN, Lou Dobbs, vowed Wednesday that his show would not carry any more reports about the candidates’ actions in the 1970s. “That’s our commitment here. We’re through with 35 years ago and we’re moving to now and the future,” said a fed-up Mr. Dobbs.

Last night, the newscaster made it a whopping eight seconds into his program before breaking his promise and mentioning the dust-up over the allegations from the Vietnam War era.