Rep. Steve Israel , D-N.Y., who nixed a Senate race last month at President Obama’s request, was the biggest donor last month to the political arm of the House Democratic caucus.

Israel, who’s in his fifth term representing part of Long Island, gave $175,000 to the Democratic Congressional Campaign Committee, completing his $200,000 in dues payments to the organization. The six-figure donation was still a relatively small fraction of Israel’s treasury, which stood at more than $1.7 million at the end of March and which Israel had hoped to use for an expensive primary challenge of interim Democratic Sen. Kirsten Gillibrand — until the White House intervened.

Israel’s donation was included in a report the DCCC filed June 19 with the Federal Election Commission (FEC) that said it raised $3.4 million in May, just ahead of the $3.2 million that the National Republican Congressional Committee (NRCC) said it raised in its FEC documents.

Both party committees are feeling the pinch from a poor economy that has depressed donor giving. The DCCC raised $23.7 million in the first five months of 2009, down 10 percent from a comparable period in 2007. The NRCC’s decline is more precipitous: its $14.4 million in receipts in the first five months of 2009 is down 39 percent from 2007.

And both organizations are carrying more debt than available cash. The DCCC has $5 million cash-on-hand and $6.7 million in obligations, compared to $3.7 million in the bank and $4 million in debts for the NRCC.

Generosity from its large membership enabled the DCCC to outpace the NRCC. The DCCC raised $970,000 from its members in May, accounting for about 30 percent of the Democratic group’s receipts for the month. The DCCC’s member contributions effectively offset the $1 million transfer that the NRCC received from the Republican National Committee, which is well-funded.

Members of Congress are often the biggest donors to national party committees because the campaign finance laws allow them to give unlimited sums from their campaign committees — and they often give far more than the $30,400 that applies to individual donors.

A dozen individuals gave that amount to the DCCC last month. One of them was Thomas Hale Boggs Jr., chairman of the prominent firm Patton Boggs and a son of the late former House Majority Leader Hale Boggs and former Rep. Lindy Boggs.

The NRCC received the maximum $30,400 last month from 10 individual donors and the Choctaw Nation of Oklahoma.

Democratic Congressional Campaign Committee

• Receipts, May 2009: $3.4 million

• Receipts, Campaign cycle-to-date: $23.7 million

• Disbursements, May 2009: $2.5 million