A top Senate Democrat has rejected as “inadequate” the GOP proposal to privately review intelligence on Iraq’s weapons programs given to the White House and Congress prior to the U.S. invasion and has again threatened to use the Senate’s rules to trigger a more wide-ranging probe if Republicans don’t respond to his concerns.

Sen. Jay Rockefeller (D-W.Va.), vice chairman of the Intelligence Committee, wants a joint inquiry by the Armed Services and Intelligence panels into the issue, with open hearings and a report released to the public at the end of the probe. Intelligence Chairman Pat Roberts (R-Kan.) has so far rejected the West Virginia Democrat’s requests, although Rockefeller vows to continue pushing his case.

“We need to be able to request additional intelligence documents, interview intelligence community and administration officials, past and present, hold closed and open hearings and prepare a final public report on lessons learned,” Rockefeller said in a statement. “A full fact-finding investigation is the usual mechanism for Congressional oversight committees like the Senate Intelligence Committee in a circumstance like this one.”

Under Senate Intelligence Committee rules, any five Senators serving on the panel can call for a formal investigation. Rockefeller claimed to have enough support from his colleagues to do that, although he has held back out of fear of angering Roberts.

Rockefeller also said he has given a formal proposal to Roberts for a joint inquiry between Armed Services and Intelligence, and he added that while Roberts agreed with his plan in principle, he refused to commit to the proposal.

“I’m not getting any hard agreements,” complained Rockefeller.

But Senate Republicans are calling Rockefeller’s comments “ill-advised” and privately suggest that he is under pressure from factions within the Democratic Party that opposed the Iraq war and are now seeking to embarrass President Bush and the Pentagon.

“He’s being pushed into this by [Sen. Robert] Byrd [D-W.Va.],” declared a top Senate Republican, speaking on the condition of anonymity. “This is his first time he’s been on the national stage and it’s not clear he can handle it.” Byrd was the Senate’s most outspoken opponent of the war.

The charges and countercharges come as the political furor over the U.S. failure to uncover Iraqi weapons of mass destruction or proof of large-scale WMD programs continues to grow. While many Democrats remain cautious about speaking out on the topic, fearing imminent discoveries of just such weapons, others believe it is time to get more aggressive on the subject.

Roberts dismissed Rockefeller’s complaints, suggesting they were more a political stunt than an effort to resolve the situation.

“Now, while I believe some of the criticism leveled on the intelligence community has been understandable … some of the attacks have been simply politics and for political gain. I will not allow the committee to be politicized or to be used as an unwitting tool for any political strategist,” Roberts told reporters during a press conference.

Roberts said the Senate Intelligence panel will begin holding closed-door hearings on Iraq next week but refused to commit to public hearings.