Evangelist Marion G. (Pat) Robertson, skirting Federal Election Commission rules, will soon become the only major prospective presidential candidate declining to disclose his campaign finances.

In addition, Robertson is running into difficulty reaching his goal of collecting 3 million signatures on a petition supporting his candidacy. After assembling petitions for more than nine months and with less than three months to go before his self-imposed Sept. 17 deadline, he has collected only 800,000 to 900,000 names, according to R. Marc Nuttle, his campaign manager.

In order to reach the 3 million goal, Robertson is abandoning the requirement that the petitions be "signed." Instead, the campaign is setting up volunteer phone banks, and if someone contacted by phone is willing to declare support for Robertson, the person's name will be added to the petition.

Nuttle said Robertson does not have to file a detailed report of his campaign finances on July 15 -- when all the other candidates are expected to do so -- because the Robertson campaign is still in the "testing-the-waters" stage. Nuttle said Robertson will disclose his finances if he announces his candidacy in September.

FEC rules permit prospective candidates to keep finances secret as long as their activities are intended "solely . . . to evaluate a potential candidacy," a stage called "testing the waters."

Once a candidate develops an organization along the lines of a presidential campaign and raises "funds in excess of what could reasonably be expected to be used for exploratory activities," the candidate must begin to make public reports to the FEC, according to the rules.

Robertson has put together a staff of 65 -- the largest of any prospective presidential candidate -- and he has raised more than $7 million, second only to Vice President Bush.

Nuttle contended that the decision not to disclose finances is legitimate despite the massive fundraising and large staff because all of the activities of the Americans for Robertson Committee are devoted to the petition drive, which, according to Nuttle, is a "testing-the-waters" activity.

The amount of money raised "may be too much for a Dole or Kemp {to justify nondisclosure} but they aren't testing the water. We are. Every single penny we've spent is toward that process."

Nuttle said no money is being spent by Americans for Robertson in the long and bitter fight in Michigan for delegates to the GOP national convention. He contended that the extensive effort put together by Robertson supporters in Michigan since the middle of last year has been a combination of volunteer activity and the work of separate conservative groups.

Last Sept. 17, Robertson financed a massive closed-circuit televised announcement to 216 meeting places across the country when he declared: "If . . . one year from today, 3 million registered voters have signed petitions telling me that they will pray, that they will work, that they will give toward my election, then I will run."

Sources said it cost Robertson roughly $3.5 million to put together the teleconference and all the subsidiary activity connected with it. There are widely differing estimates of his revenues from the event, ranging from roughly $3.5 million all the way up to $8.8 million. Nuttle declined to provide figures.

Robertson had a serious disagreement with Victory Communications, the firm that organized the teleconference, and a financial settlement of costs was not reached until February, according to various sources.

Nuttle said no decision has been made whether the campaign will accept federal matching money for contributions of $250 or less. If the campaign rejects federal money, it will not have to abide by spending ceilings and faces far less stringent auditing by the FEC. The overall preconvention spending limit is roughly $27 million, and the spending ceiling in Iowa, for example, is $750,000.

Nuttle said the campaign has between 800,000 and 900,000 names on petitions at headquarters and promises from people in the field for another million. If all those promises are kept, the campaign will have to gather additional names at the rate of 13,000 a day to meet the target.