A surge of support last week for Democratic challengers from New Jersey to California has raised the possibility for the first time that Democrats might recapture control of the Senate in next Tuesday's election.

Democratic National Chairman Charles T. Manatt yesterday said that the likelihood of a five-seat shift was "remote," and a White House official called the possibility "academic."

But campaign specialists in both parties said Democratic challengers went into the final week of the campaign within striking range, 8 percentage points or less, in five states, and another four or five seats were not much further out of reach.

By contrast, only three Democratic seats appeared to be in any comparable degree of jeopardy, and trends last week in two of the three races favored the Democrats. Republicans now hold a 54-to-45 majority, with retiring independent Sen. Harry F. Byrd Jr. of Virginia adding a 46th vote to the Democratic caucus. With Vice President Bush available to cast a tie-breaking vote for the Republicans, Democrats would need a net gain of five seats to regain the majority they lost for the first time in 26 years in 1980.

That seemed a practical impossibility, because only 13 Republican seats are up for election this year and most of the incumbents appeared upset-proof.

But a pattern of erosion, apparently linked to economic worries, hit Republican incumbents in Connecticut, Missouri, New Jersey and New Mexico, and spilled over to the California race for the seat of retiring Republican Sen. S.I. Hayakawa, moving all those contests into the potential turnover category.

Larger, but for the Democrats not insuperable, margins were reported in Delaware, Rhode Island, Vermont, Minnesota, Wyoming and Utah, all held by GOP senators seeking reelection.

The same trend boosted most of the 19 Democratic incumbents facing the voters Tuesday. Only two are now viewed as shaky, Howard W. Cannon of Nevada and John Melcher of Montana. The third vulnerable "Democratic seat" is Byrd's in Virginia, where Lt. Gov. Richard J. Davis (D) was reported edging slightly ahead of Rep. Paul S. Trible Jr. (R).

A Republican campaign official conceded that "our candidates took a lot of fire last week," but said that reports early this week indicated that the races had stabilized over the weekend or even turned around.

They cited Sens. David F. Durenberger of Minnesota and Malcolm Wallop of Wyoming as examples of incumbents who had regained the momentum in their races, after challengers Mark Dayton and Rodger McDaniel had drawn close.

But, from all reports, Sens. Lowell P. Weicker Jr. of Connecticut, John C. Danforth of Missouri and Harrison H. Schmitt of New Mexico remain vulnerable. So do San Diego Mayor Pete Wilson, who is vying with Gov. Edmund G. (Jerry) Brown Jr. for the open California seat, and Rep. Millicent Fenwick, opposed by millionaire businessman Frank R. Lautenberg, for the open New Jersey seat.

Weicker, whose opponent is Rep. Toby Moffett (D), and Wilson have been in close fights all the way, but Fenwick's chances apparently withered under a massive, self-financed Lautenberg TV blitz. Danforth and Schmitt are outspending their challengers, state Sen. Harriett Woods and state attorney general Jeff Bingaman, but still saw their leads evaporate.

Schmitt's drop was so precipitous that Democratic pollster Peter D. Hart yesterday pronounced his chances "gone," but Republicans insisted that his new TV ads are building his lead.

Hart, at a breakfast with reporters, also noted the irony that most of the Republicans who appear freshly vulnerable are from the moderate-liberal wing of the GOP, not from the ranks of President Reagan's hard-core supporters.

In addition to Weicker, Danforth, Durenberger, Fenwick and Wilson, others who fit that category and whose reelection cannot be considered assured at this point are Sens. John H. Chafee of Rhode Island, opposed by former state attorney general Julius C. Michaelson, and Robert T. Stafford of Vermont, challenged by former secretary of state James A. Guest.

One reason those moderate Republicans are in trouble, Hart said, is that the Republican message has been "schizophrenic." The national GOP advertising effort and Reagan's campaigning have been keyed to the message, "stay the course," he said, while these candidates have been "hiding from the big issue" and trying to win reelection on their own reputations and records.

Hart also faulted the Republican strategy for taking Reagan "out of the presidency and making him the chairman of the Republican Party." He said that surveys indicated that Republican prospects had diminished as Reagan took a more partisan role and tone this fall than people had seen him display previously.