New Jersey Sen. Robert Menendez — the Democratic Party’s top Senate campaign strategist for the 2010 elections — said Thursday that his party was “energized” early in an election cycle in which voters will evaluate Democratic control of the White House and Congress.

Menendez, who held his first press conference as chairman of the Democratic Senatorial Campaign Committee (DSCC), said this “is going to be a good cycle for Democrats,” who are defending 17 seats that are up for election in 2010 to 19 for the Republicans.

“We are very optimistic about the prospects in this cycle,” Menendez said.

Menendez has a tough act to follow in New York Sen. Charles E. Schumer , who headed the DSCC during the 2006 cycle, when Democrats gained six seats to claim a narrow Senate majority, and during the 2008 cycle, when the party gained at least seven more seats (pending the outcome in the disputed Minnesota election, which is now under litigation).

But Menendez — a former seven-term House member who was first appointed to the Senate in January 2006 and was elected to a full term that November — inherits from Schumer a committee that has been hitting on all cylinders in the crucial areas of candidate recruitment, fundraising and campaign organizing.

Menendez’s early bullishness about the upcoming elections owed in part to early announcements by five Republican senators that they would not run to defend their seats next year: Mel Martinez of Florida; Sam Brownback of Kansas; Christopher S. Bond of Missouri; George V. Voinovich of Ohio; and Judd Gregg of New Hampshire, who had been nominated to become President Obama’s Commerce secretary. Gregg unexpectedly withdrew his Cabinet nomination later Thursday and said he would finish his Senate term, but added that he would not run for re-election.

Menendez noted that every Democratic senator facing a regularly scheduled election in 2010 will seek re-election next year. The party’s only open seat will be that of appointed Delaware Sen. Ted Kaufman , who was appointed to fill the seat that Democrat Joseph R. Biden Jr. vacated to become vice president.

Kaufman said immediately that he would not run in the November 2010 special election to fill the remaining four years of Biden’s unexpired term. This fueled speculation that he had volunteered to be a “placeholder” for Biden’s son Beau, the state Attorney General, who is now on a tour of duty in Iraq with the Delaware Army National Guard.

With the 2010 elections still 21 months away, Menendez didn’t specify a range of possible Democratic gains. But he did note the importance of reaching 60 seats in the Senate, the threshold needed to break minority-party filibusters. The Democrats would need a net gain of one or two seats to reach 60 — depending on the outcome of the still-undecided 2008 Minnesota contest between Republican Norm Coleman, who ran as the incumbent, and Al Franken , the well-known comic entertainer who ran as the Democratic challenger.

The importance of a Senate “supermajority” was on display this week, when Democrats needed the assistance of three moderate Republican senators — Olympia J. Snowe and Susan Collins , both of Maine, and Arlen Specter , who is up for re-election in 2010 in usually Democratic-leaning Pennsylvania — to thwart a filibuster of a big-budget economic stimulus bill that Obama is laboring to push to congressional approval.

Though Specter’s reach across party lines was applauded by the White House and by Senate Majority Leader Harry Reid of Nevada, Menendez cited Pennsylvania as one state in which he expects a strong Democratic challenger to emerge. Menendez also identified David Vitter of Louisiana, Richard M. Burr of North Carolina and Jim Bunning of Kentucky as examples of Republican senators who say they will seek re-election and would face determined Democratic opposition if they do.

“I’m sure that President Obama and those who advise him politically clearly understand the value of finally getting over 60 votes in the United States Senate, after what they have gone through,” Menendez said. “And we will make collective judgments as to how to best achieve that.”

Among the five states in which Republican senators are not seeking re-election, the race in Missouri has already developed into a near-certain showdown between Democratic Secretary of State Robin Carnahan, a member of the state’s preeminent Democratic political family, and Rep. Roy Blunt , a former House Republican whip.