Rep. Clarence D. Long (D-Md.) and his Republican challenger, Helen Delich Bentley, locked in a neck-and-neck race in Maryland's 2nd Congressional District, have raised nearly $1 million between them -- a total that appears to be a record for congressional races in the state.

Long, 74, who is fighting to keep the seat he has held for more than two decades, has raised about $645,000 for the race since January 1983, according to campaign officials and reports filed yesterday with the Federal Election Commission (FEC). More than $377,000 of that total was raised this year.

According to FEC records, Bentley, a 60-year-old firebrand who formerly headed the Federal Maritime Commission, has raised $328,000 since the beginning of the year when she began raising funds for the race -- her third attempt to unseat Long in the congressional district north of Baltimore.

Officials from both camps said yesterday they would spend as much as it takes to win, likely pushing the totals to more than $1 million. Records going back to 1976 list the most expensive Maryland race as the attempt by Montgomery County millionaire Newton I. Steers to unseat Democratic Rep. Michael D. Barnes in 1980, when together they spent $916,000.

Much of Long's war chest has come from a nationwide Jewish constituency, including $35,800 since last January from pro-Israel political action committees (PACs) from as far away as Chicago and Miami. The groups view Long as one of their strongest allies in Congress, wielding power over foreign aid to Israel from his post as chairman of a key appropriations subcommittee.

Long has traveled the country, holding fund-raisers in St. Louis, New Orleans, San Francisco and other cities. One businessmen's breakfast given by a Los Angeles developer prominent in the Jewish community helped bring in more than $32,000, according to FEC reports and campaign aides. Another fund-raiser, in Queens, brought in more than $8,000 from the Greek community, which also views Long as a friend.

Bentley raised about one-third of her funds from PACs, with the bulk coming from the business community, campaign officials said. PACs for the American Medical Association and Baltimore Gas & Electric Co., for instance, have each given the $5,000 maximum allowed. Her campaign, rated by the National Republican Congressional Committee as one of the best opportunities in the nation to unseat a Democrat, was boosted by $8,000 from the committee and about $9,000 from the Republican National Committee, according to aides and FEC reports.

Other congressional incumbents from Maryland have also raised and spent substantial sums, despite less-than-formidable opposition. Barnes, for example, has raised $99,903 this year for a total of about $190,000, according to his campaign manager, Brian Barkley. So far this year he has spent about $117,500 to defend his 8th District seat against developer Albert Ceccone, who has raised just over $7,000, according to FEC reports.

"You don't really know until you get down to the last eight weeks of the campaign what kind of opposition you have, at least in terms of how much money they can raise," said Barkley, noting that in 1980 Steers poured hundreds of thousands of dollars into his campaign two weeks before the election.

In the 5th District, Democratic Rep. Steny Hoyer of Prince George's County has raised nearly $141,177 this year, on top of about $106,000 he had on hand from previous fund-raising, according to his campaign treasurer, William I. Garner Jr.

Hoyer is running against Laurel consultant John Ritchie, who has filed no documents with the FEC. Candidates must file financial statements if they raise or spend more than $5,000.

In the 4th District, Rep. Marjorie Holt (R) has raised $99,052 this year, compared to $16,271 by her opponent, Howard Greenebaum. In the 6th District, Rep. Beverly Byron (D) raised $85,530 this year for her campaign against Montgomery County lawyer Robin Ficker, a former state delegate. There was no recent FEC statement available for Ficker.