Ten months into his presidential bid, Rudolph W. Giuliani continues to work part time at the security consulting firm he promised to leave this past spring to focus on his pursuit of the Republican nomination.

Giuliani's continuing involvement with a firm catering to corporate clients makes him unique among Republican contenders. It also complicates the task of separating his firm's assets from his campaign spending.

Several of the firm's employees do volunteer work for his campaign. And Giuliani did not decide until mid-June, six months after he entered the race, to bill his campaign for the cost of the security detail traveling with him on campaign trips; before then, the firm paid the expense.

Aides at Giuliani Partners in New York and with his campaign confirmed that he continues working part time at the firm. They declined to answer specific questions about the nature of his efforts, his compensation or the amount of time he spends there.

"Mayor Giuliani spends the majority of his time on the campaign," Giuliani Partners spokeswoman Sunny Mindel said, declining to be more specific.

Federal election laws prohibit Giuliani's firm from absorbing costs or providing services that legally should be covered by political donations, campaign experts said.

"This is a lawyer's nightmare," said Republican political consultant Scott Reed, who ran the 1996 presidential bid of then-Sen. Robert J. Dole (R-Kan.) but is not aligned with a presidential campaign in this race. "I don't think the vulnerability is with voters on the level of his commitment to the race. The concern is really about FEC violations and whether anything this corporation does to help him essentially is making a contribution to run for president in the form of staff time, materials, travel billing or security."

Giuliani's aides said the firm and the campaign comply with all federal election rules and laws.

Giuliani formed the firm after he left the New York mayor's office in 2002. He built upon the reputation he earned while helping the city recover from the Sept. 11, 2001, attacks to advise clients across the world on security issues.

The clients have included civic leaders in Mexico City, who sought Giuliani's expertise on law enforcement strategies; companies that wanted to build a post-Sept. 11 security plan; and those that sought strategic advice on how to win business in the growing homeland security sector.

Giuliani's firm has grossed more than $100 million since its formation. It has employed many of the same political insiders who worked around Giuliani during his mayoral years, such as former chief of staff Anthony V. Carbonetti, former fire chief Thomas Von Essen and former corporation counsel Michael D. Hess. It also includes former FBI executive Pasquale J. D'Amuro, a highly regarded terrorism expert.

Last year, Giuliani earned about $4.1 million from the firm, according to the presidential campaign financial disclosure report he filed in May.