ALBANY – The Democratic and Republican parties are facing major internal challenges over who should be their nominee for governor of New York, with primary races all but ensured in both parties.

Having formed a fund-raising committee to back his possible bid for the Democratic nomination for governor, Nassau County Executive Thomas Suozzi, 43, will try to chip away at Attorney General Eliot Spitzer’s frontrunner status. Mr. Suozzi is expected today to announce his plans to travel around the state and meet with voters.

At the same time, Thomas Golisano, the billionaire businessman from Rochester who as an Independent opposed George Pataki in three unsuccessful bids for governor, may make known his political intentions today in Las Vegas, where his company, Paychex, is having its quarterly board meeting, according to one of his closest advisers. Mr. Golisano, who changed his party registration to Republican late last year, reportedly indicated that he would say whether he would seek the party nomination by the end of the month.

The entrance of these two candidates into the race would upend the plans of the leadership of both parties, which have tried to avoid the internal tension and expense that a primary would bring. Both candidates would be joining a race at a time when the candidates that the parties have tried to anoint are showing fresh signs of weakness.

Critics of Mr. Spitzer, 46, have questioned whether he has the temperament to be governor, after the former chairman of Goldman Sachs, John Whitehead, accused the attorney general of threatening him during a telephone conversation in April.

Mr. Spitzer, however, has a commanding lead in the polls over Mr. Suozzi and has a campaign war chest of a reported $18 million, more than four times the money that Mr. Suozzi had left over from his county executive re-election campaign. Mr. Suozzi is likely to receive a huge fund-raising boost from Ken Langone, the billionaire founder of Home Depot, a resident of Nassau County.

Another possible candidate, William Weld, the former governor of Massachusetts who is backed by the chairman of the state Republican Party, has found himself entangled in a controversy over a for-profit college that he ran in Kentucky for a brief period last year. The federal government is investigating whether the school, Decker College, committed financial aid fraud, though Mr. Weld is not accused of any wrongdoing.

Mr. Suozzi is expected to run as a reformer who will promise to address Albany’s dysfunction, lower property taxes, and fix a broken Medicaid system that is by far the costliest in the nation. He is likely to say that he will handle the state economy the way he handled the finances of Nassau County, which has received 12 bond rating increases during his tenure. He has cut the county’s borrowing in half. According to a source familiar with his campaign, Mr. Suozzi, in competing against Mr. Spitzer, will point to the attorney general’s lack of executive experience and what he believes is his failure to deal seriously with Medicaid corruption.

Mr. Suozzi, who was just sworn in for a second term as county executive, is a lawyer and an accountant who was elected mayor of Glen Cove at the age of 31. In 2001, winning in a Democratic primary against an opponent who had the endorsement of the county Democratic leadership, he became the first Democrat in 30 years to be the executive of Nassau County, which has a heavy Republican population.

Republican candidates for governor yesterday were reluctant to criticize Mr. Suozzi. Assemblyman Patrick Manning, a Republican of Dutchess County, said a battle between Mr. Suozzi and Mr. Spitzer, who is best known among voters for his crusades against Wall Street crimes, would show what the attorney general “actually stands for.” John Faso, a former Assemblyman who lost a bid for comptroller by a narrow margin in 2002, said Mr. Suozzi will “present a real competitive force for Eliot Spitzer.”

A spokesman for Mr. Spitzer, Ryan Toohey, said the campaign would “take any challenge seriously” and suggested that the attorney general would pick up the reform mantle. He said the attorney general “is excited about running an issues-oriented campaign that focuses on his record as a reformer and his vision for re-energizing the state to deal with critical issues like quality education, property taxes, health care, and job creation.”

Unlike the Democrats, the Republicans at the moment have no clear frontrunner in the governor’s race. The chairman of the state Republican Party, Stephen Minarik, has thus far failed to persuade enough county party chairmen and state delegates to get behind Mr. Weld.

Some county chairmen, saying they have little idea what the current plan is for choosing a nominee and say they have lost touch with the party leadership, appear to be taking the process in their own hands. Several county party leaders have organized a televised town hall meeting on January 21 with the candidates in Onondaga County to help delegates become more familiar with who’s running.

“It’s a little quiet, and that’s what’s bothering us,” said one of the organizers of the meeting, George Williams, the chairman of the Oswego County Republican Committee and county clerk. “We don’t know where everything is. For people who’ve been in the business for a lot of years, it bothers us.”

Ryan Moses, the executive director of the state Republican Party, said there’s “a process in place” for choosing the nominee. Last month, some county chairmen met in Albany and voted for Mr. Weld in an informal straw pole bu t many chairman from the most populous counties were absent. He said there would be another meeting of county chairmen, but no date has been set.