Maryland Attorney General Francis B. (Bill) Burch announced his candidacy for governor yesterday, formally opening what is expected to be the most timultuous Democratic primary fight in years.

"I've fought the battles for the little people and I've won them," Burch, a millionaire businessman, said from the steps of the Montgomery County Courthouse. "As governor, I'm going to continue to fight their battles."

Burch, 59, and five other Democratic hopefuls have been quietly organizing and raising funds for their gubernatorial campaigns during the past year in preparation for this September's primary.

Burch is the first well-financed and well-organized incumbent to formally declare, beginning what is expected to be a major step-up in political activity in coming weeks.

Acting Gov. Blair Lee plans to hold a major fund-raiser for his campaign next week and Baltimore County Executive Theodore G. Venetoulis is expected to announce his candidacy this month.

Other active contenders are Maryland Senate President Steny H. Hoyer (D-Prince George's), Baltimore City Council President Walter S. Irlinsky and former Maryland Transportation Secretay Harry R. Hughes.

Burch is one of the best financed candidates, having raised more than $300,000. he hopes to more than double that figure to finance a high-powered media campaign concentrating on television spots.

Last month, he distributed 18,000 copies of an expensive looking newsletter, called "The Insider," which was designed to elicit funds. His fund-raising mailings are on a computer system.

Despite his sizable campaign coffers, most political handicappers say at this point that Burch lacks the local organization and political support to defeat the incumbent Lee or the well-organized Venetoulis.

Burch is expected to draw some support in the conservative urban and rural pockets of the state where he is remembered for his fights against pornography and support of Bible reading in public schools.

The three-term attorney general, who ran twice on the same ticket as suspended Gov. Marvin Mandel, also could pick up support from some old guard politicians and interests who backed Mandel.

Burch chose the county courthouse steps in Rockville as one of four places in the state to declare his candidacy. He moved around Maryland yesterday in a private airplane and in a red, white and blue bus.

With his mane of pure white hair, trim physique and eternal tan, Burch fulfills the Hollywood image of a politician, a picture he intends to exploit in upcoming television commercials.

Several times during his one-hour press conference, he referred to himself "as a man who cares," a slogan painted across the side of his bus and used as the refrain of his campaign song.

As attorney general for the past 12 years and before that as state insurance commissioner, he said, he championed the rights of "the little people" against big businesses and criminals.

"Running for governor is just another fitht and I assure you I'm going to win," he said, as his wife, Mary Patricia Burch, and several of their children looked on appreciatively.

As attorney General, Burch has earned a reputation for defending consumer rights, protecting the environment and breaking new ground on antitrust cases against big business.

He has prosecuted several political corruption cases, fought to end racial and religious discrimination in Maryland country clubs and indicted the former fund-raising head of the Pallotine Fathers.

Because of his sensitive job as Maryland's chief law enforcer, he said, he will be circumspect about campaign contributions and will not accept money if a conflict of interest could be construed.

But he said he would accept money from lawyers who practice before state agencies and boards represented by his office as well as businesses that are regulated by his office's Consumer Protection Division.

"If you say we'll only accept a contribution from those who do not have any contact with state government," he said, "you'd say we wouldn't accept contributions from anybody."

When asked what contribution would create a conflict of interest for him, he said he would not take money from a person involved in a criminal investigation by his office.

Burch's fund-raising techniques became a source of controversy last year after newspapers disclosed he had asked members of sensitive state regulatory boards to help sell tickets for his testimonial dinner last May.

It also was revealed that Burch solicited help from lawyers across the state who had received lucrative bond counsel fees and title-searching work from his office.

"I will use my discretion when I think there is a conflict of interest," he said. "I won't accept money if a conflict is there."