Vice President Bush and Senate Minority Leader Robert J. Dole (R-Kan.) sparred anew yesterday over what is becoming the central facet of their rivalry for the Republican presidential nomination: their credentials.

Bush disparaged Dole as "part of the problem" of government for his long service on Capitol Hill. Dole said leadership was the issue and "I can't help it if he hasn't provided any."

Also yesterday, Bush asserted that he did not know about the arms-for-hostages nature of U.S. weapon sales to Iran at the time President Reagan approved them in January 1986, despite memos and documents that outlined this aspect of the deals.

With the first 1988 voting less than a month away, Bush and Dole have been waging an increasingly intense battle over their respective qualifications. Last month, they quarreled over the new arms reduction treaty. Yesterday, Bush took out after Dole directly, saying, "I'm not sure that being in Congress all your life is a part of the answer, I think it may be part of the problem." He was responding to Dole's assertion in recent days that Reagan had turned to him, not Bush, when he wanted to get something done.

"So tell him to get off my back," Bush said of Dole. "He's just begun to see the Silkworms coming across his bow."

Bush said he had served in the House "long enough to understand how it works, but not long enough to get kind of pre-opted by the situation there." He went on to list his other jobs, such as director of central intelligence, where he said that he lifted the morale of an agency "that had been battered by the excesses of the United States Congress."

"How many know foreign policy from being there, talking with these leaders, not in a photo op{portunity} with a group going over there from Congress . . . , " he said.

Dole fired back in New Hampshire. "I have a record of leadership, but he doesn't," Dole said. "I assume it's getting to him. It's going to be a big issue in this campaign. That's what it's all about: leadership. I can't help it if he hasn't provided any."

Responding to the vice president's criticism of Congress, Dole recalled that Bush spent four years in the House and twice ran for the Senate. "He certainly tried hard enough to get there," Dole said of the Bush campaigns. Dole has served on Capitol Hill since 1961.

The Senate minority leader also chided Bush for spending little time in his largely ceremonial post as president of the Senate.

"Maybe he needs to have a little more contact with his colleagues in the Senate to understand we do provide leadership, we do support Ronald Reagan, we do make a difference," Dole said.

In an appearance at the National Press Club, Bush also was questioned on his role in the Iran arms sales when he was asked whether he was aware in January 1986 that the weapons being sent to Iran were part of a deal to win freedom for the American hostages in Lebanon. "No, I did not . . . . No, at that juncture, certainly it wasn't clear," Bush said.

However, the report of the House and Senate committees that investigated the Iran-contra affair show that the arms-for-hostages nature of the deal was explicit in discussions of it at the time. Bush was present at the Jan. 7, 1986, meeting at which Secretary of State George P. Shultz and then-Secretary of Defense Caspar W. Weinberger objected, according to the congressional report.

He also was present at the Jan. 17, 1986, meeting with Reagan at which a presidential "finding" or authorization for the arms sales was discussed. "With the signing of the finding, the administration was embarked on an arms-for-hostages initiative with Iran in which the United States -- not Israel -- would play the lead role," the congressional report said.

A computer message written by then-national security adviser John M. Poindexter, on Feb. 1, 1986, and recently made public, reported that Bush was "solid in taking the position we have to try" to get hostages released. Plans were being laid at the time for the first direct U.S. arms shipments.

While maintaining that he did not know of the arms for hostage deal, Bush said yesterday, "I stood with the president." He added that he would not divulge what he told Reagan in private. "I'm not a kiss and teller," he said.

But Bush also said he had "reservations" about the arms deals. In the past, Bush has said these were concerns over the prominent role of Israel in the deals. Bush said yesterday that Poindexter had testified under oath about these reservations. However, the substance of Poindexter's description of the Bush concerns was classified "top secret" by the White House and has never been released.Staff writer Edward Walsh contributed to this report.