Sen. Bob Menendez (N.J.) this week prodded nervous members of the Senate majority to step up their giving to the Democratic Senatorial Campaign Committee as he girds for midterm elections that have Democrats on the defensive.

Sources said the DSCC chairman has been straining to keep ahead of his Republican counterparts in a tough fundraising climate characterized by donor fatigue and supporters feeling less generous in a weak economy.

Menendez said Wednesday that Democratic Senators have been “extremely” helpful to the DSCC this cycle. The committee still led the rival National Republican Senatorial Committee in fundraising at the end of April — but narrowly — and Democratic Senators continue to far outpace GOP members in contributions to their respective campaign committees.

But with three Senate Democratic leaders focused on their re-election bids and the prospect of continued political headwinds as Nov. 2 approaches, Menendez is pushing his caucus to pick up the pace. According to one knowledgeable Senate Democratic aide, during the leadership’s regular Tuesday morning meeting, Menendez told colleagues that they need to become more involved, including making fundraising calls and donating from their personal campaign accounts.

Later that day, Senate Majority Whip Dick Durbin (Ill.) issued a rallying cry to fellow Democrats during the weekly policy lunch, telling colleagues that Menendez needs help. Durbin personally pledged to transfer $50,000 from his campaign to the DSCC. His appeal received “a tepid response,” the Democratic Senate aide said.

After two consecutive election cycles that found Senate Democrats in the driver’s seat and the DSCC playing offense on its way to a pickup of 14 seats, 2010 has seen the momentum shift to the Republicans. Senate Majority Leader Harry Reid (Nev.) and Conference Secretary Patty Murray (Wash.) appear to face tough challenges, with the GOP positioned to gain, if not hold its own, in key open-seat contests. Democratic Conference Vice Chairman Charles Schumer (N.Y.) is also up for re-election this year.

As he seeks to build a protective firewall, Menendez is leaning heavily on Durbin, the only senior Member of the Democratic leadership team other than the DSCC chairman, who is not up for re-election this year. Durbin has hosted five Chicago fundraisers for the committee this cycle, raising just under $2 million in Illinois alone. He has hosted seven events in Washington, D.C., and three additional fundraisers in other parts of the country.

Durbin is scheduled to headline a DSCC fundraiser in Indiana next month. He said Wednesday that he’s been to Washington, Montana, Nebraska, North Carolina and Virginia to raise money for Democrats and that he’s headed to Missouri soon.

“I’ve been asked to do more things. But I expected it. I’m working a little more at the DSCC and doing more speaking,” Durbin said. “I expect to do that because each of my other colleagues has their own responsibilities in their home states.”

Menendez said Durbin’s assistance has been “significant.”

“Sen. Durbin has been very helpful, has raised money for us in Chicago, has contributed a significant sum of his own campaign accounts, and we often call on him to travel, so we’re going to continue to look towards him and rely upon him,” the New Jersey Democrat said.

In 2008, Schumer, who was then the DSCC chairman, brought in Menendez to serve as the committee’s vice chairman. This cycle, Reid has decided against naming a traditional vice chairman, although Sen. Amy Klobuchar is serving as DSCC vice chairwoman for policy and outreach. The Minnesota Democrat described her role as speaking at events around the country.

To compensate for the lack of a dedicated vice chairman, Democratic Senators have been rotating into the role each month, during which they spend time at the DSCC raising money and organizing activities. Menendez said this method fosters more participation.

“A permanent vice chair role is really a choice for the Majority Leader. And so the bottom line is that we did not come to a conclusion to have a permanent vice chair,” Menendez said. “So, in essence, we get a vice chair every month who engages and commits for that month, which creates a greater intensity because it’s only a limited commitment of call time, of helping us organize.”

Sen. Sheldon Whitehouse, who has served as a monthly vice chairman, said the position is intended to be “an immediate go-to person to take some of the load off Bob Menendez in terms of rounding up colleagues for events that need bodies at them, in terms of inspiring folks to come to the telephone sessions over there.”

The Rhode Island Democrat said the monthly vice chairmen have developed “a little bit of competition” over who raises more money and who brings the best home-state food. Whitehouse said he enticed Members with stuffed quahogs — a kind of clam — and a local Rhode Island soda.

Some Democratic strategists dismissed the significance of the vice chairmanship, noting that Schumer did not have one during the successful 2006 cycle. At the NRSC, Sen. Orrin Hatch (Utah) is serving in his second consecutive stint as vice chairman.

Whitehouse said the rotating position “increases member involvement, and it’s something new, and people who can’t commit to months of this nevertheless come in and put in extra time in one month.” He said continuity in the position is not a problem because “the staff provide continuity, and Bob Menendez provides continuity.”

Whitehouse said he did not feel more urgency to raise funds for the committee this cycle than he did during the 2008 cycle, despite the political heat Democratic incumbents face at home.

“At this point, I’m not feeling a lot of pressure because I think I’m one of the people who they look on as pretty reliable,” said Whitehouse, who noted that he spends a couple of hours a week at the DSCC. “Last year, the urgency was associated with the prospect of winning seats. This year, the urgency is associated with not losing seats, so there’s that difference.”

Democrats hold a narrow lead in the Senate money race — since January 2009, the DSCC has raised $61.8 million and the NRSC has raised $60.5 million — but as of April, the two committees were reporting essentially the same amount of cash on hand, $17.1 million, and the Republican committee outraised the Democrats last month by more the $1 million.