The New York Democrat began making calls to New Hampshire activists over the weekend and Iowa Democrats on Monday.
Gordon Fischer, a Des Moines lawyer who formerly chaired the Iowa Democratic Party, said he had gotten a message from Clinton's staff inviting him to dinner in Washington next week. Fischer said he would be unable to attend and did not know who else had been invited.
Clinton spoke to New Hampshire Gov. John Lynch last week, Democratic officials told The Associated Press.
Bonnie Campbell, a former Iowa attorney general who served in the Justice Department under President Bill Clinton, said she spoke to Clinton twice on Monday. Campbell's husband, Edward Campbell, is a former chairman of the Iowa Democratic Party.
"It was highly exploratory about '08," Campbell told The Associated Press. "She knows a lot about Iowa. I have already told her I would support her. We've known her for a very long time."
Iowa, whose presidential nominating caucuses are still 13 months away, presents a complicated challenge for Clinton.
Iowa Gov. Tom Vilsack announced last week that he would seek the Democratic presidential nomination, and former North Carolina Sen. John Edwards, the 2004 Democratic vice presidential nominee, has made extensive inroads in the state as he's readied his own likely 2008 bid.
A June Des Moines Register poll found Edwards leading among likely caucus goers, 30 to 26 percent. Massachusetts Sen. John Kerry, the 2004 Democratic presidential nominee, placed third with 12 percent, and Vilsack won 10 percent.
Clinton has also made several key campaign staff hires in recent days, and in her outreach to New York Democrats convinced at least one she soon would become a candidate.
"I don't think she ever outright said it, but there's no doubt in my mind that she's going to run," said Rep. Joseph Crowley, who spoke with Clinton on Monday. "It was a very exciting and exhilarating conversation. I don't know how often it happens in a lifetime when someone calls you up and says, 'I want you to know I'm doing this and I want your support."'
The New York senator, who tops every national poll of likely Democratic candidates, had tried to keep private many of her overtures to supporters and new staff. The deliberations have started to become more public in the last week as the field of likely contenders has begun to expand.
In head-to-head match-ups against a leading potential GOP opponent, Sen. John McCain, Clinton runs even with the Arizona senator or slightly behind him.
The Democratic race for the nomination is growing more crowded almost daily. Indiana Sen. Evan Bayh said Sunday he was forming a presidential exploratory committee. And, Illinois Sen. Barack Obama has attracted tremendous publicity around a possible run, vaulting to second place behind Clinton in many polls even though he is relatively new to the national political scene.
Obama's emergence as a potential contender has led some observers to suspect Clinton has stepped up her timetable for making a decision about a run. Her aides dismiss that notion, saying she is observing the timetable she has long planned.
Other likely candidates include New Mexico Gov. Bill Richardson; and Sens. Joseph Biden of Delaware and Chris Dodd of Connecticut.