"Four more independent people, you won't find. And I think that's what people want," he said.
Through a spokeswoman, Mikulski said she will campaign on her achievements during her first two terms in the Senate.
"I'm proud of my record. I'm running a vigorous campaign and I look forward to taking my message to the voters of Maryland," she said.
Liebmann, a partner in the firm Liebmann & Shively, has behind-the-scenes government experience. As a member of Gov. Harry Hughes' administration, he wrote a memo in 1984 warning of instability in the savings and loan industry - an industry that crashed in the late 1980s.
Liebmann said Mikulski is too beholden to special-interest groups and practices grievance politics.
A prime example, he said, is education. Mikulski has rejected reforms opposed by the teachers unions, he said. He advocated allowing states to provide vouchers and other incentives to break the public school "monopoly" on education.
Liebmann said the federal government has interfered in disciplining unruly students, citing a 1997 amendment that would have eliminated limits in the length of suspensions school systems can impose on emotionally disturbed students.
The amendment failed with the help of Mikulski, he said.
If Liebmann gets the GOP nomination, he will face an admittedly uphill battle against the popular Mikulski. She has coasted to two landslide victories and boasts one of the largest campaign war chests in Congress.
"I don't think it's necessary to outspend her," he said. "I don't think she needs to be drowned in television commercials."
The Republican primary is Sept. 15 and the general election is Nov. 3.
So far, two Republicans have filed, Montgomery County lawyer Robin Ficker and Baltimore County contractor Thomas L. Scott. Carroll County businessman Kenneth L. Wayman also has announced his candidacy.
The filing deadline is July 6.