Hal Daub rode Ronald Reagan's coattails to Washington. They were just strong enough for him to carry his Omaha congressional district with 53 percent of the vote.

This year he has the same opponent--in a area with 22,300 more Democrats registered than Republicans--and Reagan's coattails are gone.

But Daub has one significant advantage: money. According to Federal Election Commission reports, he has raised almost 10 times as much money as Democratic nominee Richard M. Fellman--$113,593 for Daub, compared to $11,312 for Fellman.

Ominously for the Democrats, Daub's case is typical of marginal congressional districts around the nation. FEC records indicate Republicans are piling up huge fund-raising leads in these districts where money could be a decisive factor on Nov. 2.

GOP leaders are hoping that this financial edge, which they can control, and an upturn in the economy, which they can't, will enable them to pad their majority control of the U.S. Senate and minimize their losses in the House, possibly to as few as a dozen.

Their fund-raising lead is additionally significant because Democratic candidates, as individuals, traditionally have raised more money than Republicans. Democratic strategists have counted on that to offset the gigantic war chest accumulated by national GOP groups--the Republican National Committee and the Congressional and Senate campaign committees--which are expected to outspend their Democratic counterparts by more than 10 to 1 this year.

FEC reports on fund-raising through April 1, however, indicate that Democrats aren't moving ahead in fund-raising in some districts where the closest races are expected.

Three races where former Democratic congresssmen are trying to recapture seats they lost in 1980 are cases in point. Republicans hold impressive fund-raising leads in all three, outdoing Democrats $659,662 to $242,791.

Northern Virginia Rep. Stanford E. Parris has raised $251,497, much of it from business political action committees. His opponent, Democrat Herbert Harris, has raised $85,313.

In Pennsylvania, Rep. James K. Coyne, who won with just 51 percent of the vote in 1980, has raised $178,456, compared to former Democratic congressman Peter H. Kostmayer's $83,350. In Michigan, Rep. Jim Dunn holds a similar fund-raising lead over Bob Carr, the three-term Democratic congressman he barely defeated in 1980.

Democrats are at a decided money disadvantage in other districts with vulnerable incumbents. Reps. Paul Findley (R-Ill.), Lawrence J. DeNardis (R-Conn.) and Thomas J. Tauke (R-Iowa), all of whom represent marginal districts, hold large fund-raising leads over attractive Democratic challengers.

Incumbents normally have an easier time raising money than challengers, which may partially account for the Republican advantages. But incumbency isn't working in several districts now held by Democrats.

Rep. Les AuCoin, for example, is a popular Oregon Democrat, first elected in the Watergate class of 1974. In 1980, he raised five times as much money as his Republican opponent and won two-thirds of the vote in his district. But this year his GOP opponent, William J. Moshofsky, has raised $203,842. AuCoin has raised $137,565.

Besides the money they raise themselves, Republican candidates can count on substantial help from their party.

With a $37 million budget, the National Republican Congressional Committee will have $6 million to give directly to candidates. The Republican National Committee plans to kick in $5 million more for House candidates.

If this $11 million were distributed equally over the 435 House races, each district would get $25,287. But things don't work that way in politics. Democrats hold a hammerlock on some districts, Republicans on others, making it pointless for the national parties to devote much attention to them.

So both parties target certain races. Republicans plan to target about 100 House races. They will have enough money to give each the legal limit. This, according to the FEC, totals $56,880 in each for the national parties. State parties can give $10,000, an amount which the RNC and NRCC plan to pick up in some cases.

The amounts are even larger in Senate races. Here, the legal limit is based in part on state population. It ranges from a low of $101,260 in small states to $1,339,246 in California, the most populous state.

The Republican Senatorial Campaign Committee claims to have enough money to give each nominee the legal limit, or more than $10 million. Its Democratic counterpart has only $1.2 million to divide among all its candidates--not enough even to give the maximum to the Democratic nominee in California.

The Democratic Congressional Committee has $1 million to give directly to its candidates. It decided to put this into 80 targeted races. This amounts to $25,000 per race, or less than half what Republicans plan to funnel into each of their targeted races. The Democratic National Committee doesn't have any money for House races.

Democrats, according to spokesmen, won't have money to put into dozens of potentially promising races, some of which are long shots. It is unlikely, for example, that Democrats will have any money to give to attractive candidates like Ruth Clausen, who organized the 1976 presidential debates when she was president of the League of Women Voters.

Clausen, an assistant secretary of energy in the Carter administration, is running against second-term Rep. Toby Roth (R-Wis.), who is not considered to be in particular trouble, but could be if the economy worsens and Clausen mounts an effective challenge.

Democrats also won't be able to afford any direct aid for races in some areas where they have a registration edge. In Omaha, for instance, Democratic candidate Fellman, who ran 14 percentage points ahead of Jimmy Carter two years ago, says he is uncertain if he'll get any help from his national party.

Fellman was outspent by more than 2 to 1 in 1980, and fears he will be at a 3-to-1 disadvantage this year.

"The amount of money will become an issue in this race," he says. "There's a real question of whether an election can be bought and sold."

Rep. Tony Coelho (D-Calif.), chairman of the Democratic Congressional Committee, is an open admirer of the highly professional fund-raising apparatus Republicans have put together. He says it will take years for Democrats to duplicate it. Meanwhile, Democrats are at a decided disadvantage.

"Republicans will be able to gamble this year, and we can't," he says. "They can afford to waste money and take chances. We can't."

By all estimates, 1982 will be the most expensive congressional election year in history.

Until the last decade, House campaigns normally were mom-and-pop operations, seldom costing more than $100,000. According to a study by Congressional Quarterly, the average House campaign in a suburban district in 1980 cost $197,000 and the average urban district race cost $155,000.

This year, Eddie Mahe, a respected Republican campaign consultant, says, "My feeling is you can't be serious without $400,000 to spend, and indeed, you'll need closer to $500,000 in many places."

One of Mahe's clients, Rep. Manuel Lujan Jr. (R-N.M.), who won with only 51 percent of the vote in 1980, hopes to raise $600,000. FEC reports indicate he has already collected $222,433. His best-known Democratic opponent, state treasurer Jan Alan Hartke, son of former Indiana senator Vance Hartke, has raised just $19,233.

Democrats are doing better in critical open seats--new seats created through reapportionment and those where incumbents are not seeking reelection.

In 44 of the 56 open seats, Republicans have a clear fund-raising lead in 22, Democrats in 20, with the other two about even, according to FEC records.

NRCC political director Joe Gaylord says Republicans will have the edge in states with late primaries and redistricting. "There won't be time for dress rehearsals in many places this year, and the side that reacts quickest to a changing situation is always best off," he says. "That's why it helps us. We have more money and can react."

The Republican arsenal gives them an edge in several other areas. They have a larger field staff, a more sophisticated research and communications division, and a more extensive training and candidate recruitment program than Democrats. They also have money to conduct polls and a major national television advertising campaign.

Coelho worries about the impact all this will have on the election.

"I'm fearful that we'll have the issues, the enthusiasm, and all the heartaches this administration has caused going for us, and end up losing because of their ability to market a product," he says. "It's scary what money can do in 1982."