The partisan fray over John Tower's nomination as defense secretary erupted on the Senate floor Wednesday even before debate began as Democratic leader George Mitchell announced his opposition to the Republican.

The declaration by Mitchell, of Maine, dimmed confirmation prospects for the embattled former senator from Texas and immediately set off a blast at the process of examining Tower from conservative Sen. William Armstrong, R-Colo.Tower, in an appearance at the National Press Club, made a barbed reference to the controversy at the outset. "I think that this doesn't really look much like a lynch mob, but as the saying goes, we'll know more later," he said. Tower devoted his speech to defense policy issues, the matters that he said "normally occupy the mind of the nominee of secretary of defense."

The White House said President Bush would promote Tower's case in an afternoon speech of his own. "We'll keep up the good fight and see how it goes," said presidential press secretary Marlin Fitzwater, reiterating Bush has no intentions of withdrawing Tower's name.

The White House and Senate Republicans were pushing the "fairness" issue in the high-stakes political battle, looking to the public to mount pressure on wavering members of the Senate's Democratic majority.

Though the formal debate on Tower was to start in the afternoon, Senate GOP leader Robert Dole of Kansas said Republicans were still weighing whether to seek a delay until Thursday. That almost certainly would push a final vote into next week, giving the White House more time both to lobby undecided senators and to take its "fairness" arguments to the public.

Mitchell, whose vote as Senate leader - combined with the opposition of Armed Services Committee Chairman Sam Nunn, D-Ga., - was closely watched by wavering Democrats, declared that after reading the FBI background report on Tower he decided the Republican "should not be confirmed as secretary of defense."

Speaking to an almost empty chamber about the allegations of misconduct against Tower, Mitchell said occasional abuses of alcohol could be ignored "but when the lapses in judgment form a pattern of many incidents spanning many years, and when there is insufficient evidence to demonstrate that the pattern has been broken, then there are reasonable grounds" to object.

Mitchell acknowledged conflicts in the FBI evidence when the 300-page report is viewed in the most favorable light, but he said, "There is surely no basis for the claims by some of the nominee's supporters that there is nothing but rumor and innuendo in the record."

Acknowledging Tower's professional credentials, Mitchell raised conflict-of-interest questions about the fact that Tower, after leaving the Senate, was paid handsomely as a defense consultant at a time "while it was widely assumed that he might be a nominee for defense secretary."

Mitchell said he told Bush that he hoped the fight over Tower, which began breaking down into partisanship after a party-line rejection of the nominee by the Armed Services Committee last week, would not harm relations between the Senate and the White House.

Armstrong immediately responded to Mitchell by urging his colleagues to use only facts in judging Tower. While not referring to him by name, Armstrong noted former Sen. Gary Hart of Colorado was defeated for the 1988 Democratic presidential nomination because of specific information about personal misconduct.

With Tower, Armstrong said, the Senate is dealing only with "allegations hinted at, never made."

Tower's weekend pledge to spurn alcohol won him some praise but clearly had not won over key senators by Wednesday. Florida Sen. Bob Graham, one of the Democrats personally lobbied by Bush Tuesday, said he remained skeptical after reading the FBI report.

"The trouble with the pledge is that this is not the first time John Tower has made statements that this was going to be the end of (his) abuse of alcohol and that (he) will discontinue this pattern of behavior in the future," Graham said on CNN. "That is in the (background) material."

Tuesday night, Dole and Sen. John Warner of Virginia, ranking Republican on the Armed Services Committee, went to the White House to brief Bush and Tower on the continuing apparent gloomy prospects for the nomination.

Dole and Warner later outlined GOP strategy to reporters. Dole insisted his party did not want to stall but said it would "take more than a couple of days" of Senate debate because "we'll have plenty to say."

Sen. James Exon, D-Neb., noted a delay would help Bush with "arm-twisting" and would indicate "an all-out battle." But he predicted defeat in any case and concluded, "I think that's a very unwise decision for the president."

Dole said Republicans remained optimistic they could stop Tower from becoming only the ninth Cabinet nominee rejected by the Senate. If defeated, he would be the first rejected since Lewis Strauss, President Eisenhower's choice to be commerce secretary in 1959.

An ABC News-Washington Post poll Tuesday found 52 percent of those surveyed thought the Senate should confirm Tower while 43 percent said he should be rejected. But 50 percent said they thought Bush should not have nominated him in the first place.