The only avowed lesbian state legislator in the country announced last night she will tackle the only black legislator in the U.S. Senate for his job.

Elaine Noble, the liberal Democratic state representative from Boston who gained national notice as a champion of homosexual rights, is a favorite to win the nomination to face liberal Republican Sen. Edward R. Brooke (R-Mass.) in November in what is fast becoming one of the liveliest congressional battles in the nation.

Despite a tag as a "one-issue" candidate for spearheading several ill-fated drives to push through state legislation to prevent discrimination against homosexuals, the two-term legislator has developed a respected reputation at the state House here as an ardent fighter for measures to aid women, the elderly and urban poor.

At a recent fund-raiser, Noble received the support of the State House Democratic leadership and nearly every constitutional officer in the state as well as that of the U.S. House Speaker Thomas P. (Tip) O'Neill Jr., who said, "she'll make a tremendous senator; if she is the nominee I'll support her."

She will face one of her colleagues from the Massachusetts House in the Democratic senatorial primary, - state Rep. Michael Connolly of Boston - best known for walking from Pittsfield in the western part of the state to Boston in 1977 to dramatize his drive to limit the length of office for state officials to a maximum of 12 consecutive years.

On the Republican side, the acknowledged potential spoiler for the heavily favored Brooke is radio and television talk show host Avi Nelson. Although his ideology is more closely linked to the conservatism of the dwindling Republican Party here, Nelson was reportedly pressured by Massachusetts GOP leaders to stay out of the race.

Although Brooke, the only remaining major Republican officeholder in the state, frequently acts and votes more like a Democrat than a Republican, his party leaders have apparently acquiesced to the notion that a popular, liberal Republican senator is better than no Republican senator.

Brooke's high ratings in the polls and string of successful statewide races are not expected to do Noble's candidacy any good outside of the Boston area.

"Noble may be okay on Beacon Hill and the Back Bay [her district in Boston] but I don't know if gay rights is gonna sell in Pittsfield," noted one political observer.