The wolfpack is circling here. The same word is out on all political grapevines: Sen. Edward W. Brooke's (R-Mass.) reelection campaign is in deep trouble, so much so that a right-wing challenger no one took seriously a few months ago is now given a good chance of upsetting him in the Republican primary.

Democrats, who not long ago were conceding defeat at Brooke's hands, can hardly contain themselves. "A sort of wolfpack mentality" has set in, Mayor Kevin White said the other day.

The list of Democrats who (1) want to jump into the race (2) already have or (3) wish they had earlier is about as long as a Boston marathon.

"What looked like an election that would put everyone to sleep a few months ago has turned into the most bizarre race imaginable," said one candidate, state Rep. Elaine Noble. "I call it Looney Tunes Presents."

When Noble, the only state legislator in the country who is an acknowledged lesbian, made her decision to enter the race months ago, "everyone told me I was crazy," she recalled. "They said things like, 'Ed Brooke can't be beat,' and, 'What is a good liberal like you doing running against the only black in the U.S. Senate?'"

Now some of those people are in the race.

What has happened?

"I think Ed Brooke's analysis is correct," Noble says. "They smell blood and jump in."

There have been rumblings that some liberal Republicans would like Brooke, who is enmeshed in a series of controversies over alleged financial improprieties and a "misstatement" during his divorce proceedings, to step aside gracefully. This would enable some other liberal Republican, such as Eliot L. Richardson, to get into the race.

But Brooke has made it clear that he has no intention of dropping his campaign for a third term. "I want you to know, if they want this seat in the United States Senate, they are going to have to take it from me," he told a cheering crowd of blacks in an emotional speech last week.

Most of Brooke's troubles stem directly or indirectly from his divorce from his Italian-born wife of 31 years. No opponent, however, mentions his divorce directly. Instead, they talk in code words, using phrases like "integrity in government," "trustworthiness" and "vulnerability" when they talk about the senator.

By popular political wisdom, Brooke has become more vulnerable almost daily since May 25, when he told The Boston Globe that in divorce proceedings, he told had testified falsely about $47,000 his mother-in-law had turned over to him.

One allegation of impropriety has followed another since then, until state Republican Chairman Gordon Nelson, an avowed conservative, called a new conference last week to dcery what he called a "climate of hysteria" over Brooke's divorce. He accused the media of "participating in a lynching party."

The immediate beneficiary of Brooke's troubles is a baby-faced 35-year-old arch-conservative talk-show host, Avi Nelson, who is Brooke's chief opponent in the Republican primary.

Nelson is against almost everything Brooke stands for. While Brooke has voted for the Panama Canal treaties, son supports it. While Brooke has vote for the Panama Canal treaties, federal funding for abortions and handgun controls, Nelson opposes them.

Brooke won his two elections to the Senate handily, relying heavily on support from Democrats and independents. But his chief political adviser, Roger Woodworth, says 30 to 38 percent of the vote in any Massachusetts Republican primary is a hardcore conservative vote, which Nelson can rightly be expected to pick up. "We expect Nelson to be tough," he said. "We've always expected that."

Woodworth is banking that "time is on our side. If this was Oct. 23 instead of June 23," he said, "I think all bets would be off. A helluva lot of waves are going to wash up against the beaches by October. We think the people by then will know all the facts and the results will be okay."

A good many Democrats and some Republicans disagree. They point out that Brooke is facing four official inquiries, each with the potential of opening up further political wounds.

"A new shoe seems to be dropping every day," says one bothered Republican. "It all depends on how many shoes you have. Most people have two. What happens when the third one drops?"

Three major candidates have entered the Democratic primary in recent weeks, further muddying the waters. There are now five Democrats in the race who are considered significant, and three who are viewed at minor. In addition, the possibility is still open that Mayor White may enter.

Democrats may chew one another up. Three candidates - Noble, U.S. Rep. Paul Tsongas and Massachusetts Secretary of State Paul Guzzi, a former Harvard footballstar - are vying for the liberal vote. They have one arch-conservative opponent, Howard Phillips, a Republican-turned-Democrat. He is best known as the man Richard Nixon brought to Washington to dismantle the U.S. Office of Economic Opportunity six years ago.

The fifth mayor candidate is Boston school committeeman Kathleen Sullivan Alioto, the new wife of the former mayor of San Francisco and the daughter of the owner of the Boston Patriots.

Guzzi, who announced his candidacy Thursday, is considered the favorite, followed by Tsongas and Alioto.

The race has been devoid of any real issues.

"Looks more like an issue of People magazine than a campaign for the U.S. Senate." Tsongas said last week. "The only things people are talking about are Brooke's divorce, Kathleen Sullivan's Rolls Royce [she showed up at a parade in working-class Dorchester last week in a black Rolls Royce with California license plates] and Paul Guzzi's opportunism."

This week will be a crucial one for Brooke. His former wife has to decide if she wants to accept the offer for a new divorce that a Middlesex County judge made after he found Brooke had given "false testimony" in his first divorce case.

Brooke, meanwhile, has gone on the offensive, attacking the media and telling audiences that he is a victim of a post-Watergate climate. Nowhere was this more evident than at a meeting of the True Benevolent Protective Order of the Elks Friday.

It was a black, middle-class crowd made to order for Brooke. He was introduced as a martyr in the making, a block, like the late Adam Clayton Powell, whom the establishment was trying to drive from office.

Brooke's speech was a masterpiece of political eloquence. Sounding at times, like a Baptist preacher, he touched on almost every issue and symbol on the agenda of black America for the last two decades - jobs, open housing, the 1968 riots, the civil rights marches through the South, the Bakke reverse discrimination case. He quoted from the Bible and the Rev. Martin Luther Kink Jr. He pled for prayers of understanding of his family problems.

"I want you to know that not one thing that I have done in my private life, not one action that I have taken, has ever betrayed your public trust . . . I have hurt to one. I have done nothing that I am ashamed of, or anything you need to be ashamed of me," he said.

He ended the emotional speech, which was repeatedly interrupted by loud applause, by quoting from a speech that he made the previous night before a boys state group. "A quitter never wins," he said, "and a winner never quits."