Here in this raw, bustling little Fort Worth suburb, site of a jarring battle to make Congress into the image of Ronald Reagan, Republican challenger Richard Armey bumped hard one morning against the barrier protecting one of the most vulnerable members of the Democratic class of '82.

Jean Lee, 42, a short, curly-haired worker at the Stratoflex plastic hose plant, eyed the tall economics professor with the dark profile of a young Victor Mature. "I really have never heard of you before," she said.

And what had she heard of the incumbent, Rep. Tommy J. Vandergriff (D-Tex.), the courtly former car dealer and mayor who squeezed into his first term in Congress two years ago by 344 votes, the thinnest margin in the country?

"I know him," said Lee with a smile, happy to be on familiar ground. "He built Arlington."

Among a bumper crop of 61 Democrats (compared with 24 Republicans) elected to the U.S. House of Representatives for the first time in 1982, Vandergriff was expected to suffer the uncertain fate of a class elected in a mid-term moment of doubt about the Reagan presidency, before the resurgent economy put the president and his party back on top of the national polls.

Throughout the country, Republican strategists have been looking for vulnerable freshman Democrats to cull from the roster in their congressional infancy.

The Democratic victory of 1982, said Steven Lotterer of the National Republican Campaign Committee, "was not pro-Democrat, it was anti-Republican." The freshman Democrats had campaigned on a platform of "we've got to get rid of the tax cuts, we've got to stop Reagan," said Lotterer, whose committee is supplying advice and money to dozens of Republican challengers. "That's coming back to haunt all of them now because the economy is turning around."

But what seem in Washington to be strong winds of national change often fail to shift the granite facts of local issues and personalities that influence congressional races. A Reagan avalanche could bring some surprises. But many of the freshman Democrats once thought to be in trouble now seem near reelection.

One reason is redistricting. Congressional redistricting, mostly controlled by Democratic state legislatures, contributed to the success of Democrats in 1982 and later adjustments have done little to hurt the new incumbents.

Vandergriff's 26th Congressional District, an oddly shaped collection of suburbs between and north of Dallas and Fort Worth, was supposed to elect a Republican when first created in 1982 -- unless Vandergriff decided to run.

A wealthy, conservative businessman who had served 26 years as mayor of the suburb of Arlington, Vandergriff, now 58, was a force to ruin the plans of the brightest political demographers. He was famous for turning an 8,000-population crossroads town into a city of 160,000 with a major-league baseball team, the Texas Rangers, and a world-class theme park, Six Flags Over Texas. With a broadcasting degree from the University of Southern California, Vandergriff even saved the city a lot of money by serving for a spell as the Rangers' unpaid color announcer.

In 1983, Texas Democrats fiddled with the district boundaries some more, this time giving Vandergriff all of his former Arlington base instead of just two-thirds and increasing the number of Democrats in the 26th District by about 2 percent.

In California, site of eight congressional districts represented by freshmen Democrats, the Democratic-controlled legislature did its work so well that a leading Republican strategist in Los Angeles laughed derisively at the suggestion that his party might pick up any of those seats.

Many freshman Democrats labeled vulnerable by national GOP officials like Lotterer see little reason for worry. In Minnesota, Democratic Reps. Timothy J. Penny, 32, and Gerry E. Sikorski, 36, won election with 51.2 and 50.8 percent of the vote, respectively, and face strong challenges from energetic, conservative Republicans of their generation -- businessman Keith Spicer, 34, and attorney Patrick Trueman, 35.

Sikorski retains the advantage of a strong Democratic district. Penny, running in the state's more rural southeast, has a seat usually reserved for a Republican, but he has won success by classing himself as a "compassionate conservative" who supports the Equal Rights Amendment but opposes legalized abortion.

A freshman Democrat in conservative Nevada, Harry M. Reid, 44, has turned personal wealth, kind words for Reagan and votes for the MX and against ERA to his advantage in his rematch with Republican Peggy Cavnar, 39.

Far more endangered freshmen on Republican hit lists include Rep. James F. McNulty (D-Ariz.), who faces the same challenger he beat by less than 2,500 votes in 1982, and Rep. Peter H. Kostmayer (D-Penn.), who is serving his third nonconsecutive term in a district solidly for Reagan. He has a well-organized and well-financed Republican challenger in David A. Christian.

Rep. James R. Olin, 64, won his Roanoke-area district by 1,655 votes in 1982 and may be the most endangered Democrat in Virginia. He faces a stiff challenge from former state senator Ray Garland, 50. Rep. Herbert H. Bateman of Newport News is one of the few freshman Republicans in the country thought to be in any trouble.

Other endangered freshman Democrats include North Carolina Reps. Robin Britt and James McClure Clarke and Rep. Thomas R. Carper of Delaware, who faces Elise R. W. du Pont, wife of the state's Republican governor.

An official with the Democratic Congressional Campaign Committee who asked not to be identified said the freshmen in the most trouble are McNulty, Rep. Bruce A. Morrison (D-Conn.) and Rep. Frank McCloskey (D-Ind.).

McCloskey, 45, a former mayor of Bloomington, is trying to hold onto an extremely volatile district. His Republican challenger, state Rep. Richard D. McIntyre, 27, became famous for persuading the state to put aside a portion of its surpluses to meet future deficits.

The National Republican Congressional Committee has collected reams of material on inconsistent votes by freshman Democrats for use by their opponents.

In the struggle to unseat the popular Vandergriff, the Republican challenger, North Texas State economics professor Armey, 44, has been circulating sheaves of alleged Vandergriff "flip-flops" on issues. "I like Tom," he told a Kiwanis Club luncheon on a rainy afternoon here. "It's just that he doesn't represent the views of the people of the 26th District."

According to Armey's campaign manager, Kerry Knott, 24, a former Right-to-Work organizer from Alabama, the Republican challenger's campaign has targeted tens of thousands of new voters who have arrived in the booming suburban district since 1982. "Most of them are Republicans, and they don't know who Tom Vandergriff is," Knott said.

Vandergriff, recognizing the temperament of his district, has advertised his support for the MX missile, school prayer and much of the President's economic program. He even declines to say if he will vote for Walter F. Mondale, his party's presidential nominee.

A recent Armey handout roasted Vandergriff for voting to delay the third year of the Reagan tax cut, supporting the nuclear freeze and supporting the domestic-content bill that would require use of U.S.-made parts in foreign cars.

At a reception on the top floor of the First State Bank building in Denton, a once-rural community still considered a Democratic stronghold, Vandergriff -- without prompting -- spent much of his time defending himself against Armey's attack on his voting record.

The vote to delay the tax cut was part of a deal to win $6 billion in federal spending, he said. The domestic-content bill was "to give our trade negotiators a bargaining chip; to indicate there is significant protectionist sentiment in the country." He said he supported the freeze as a way "to maintain communication" with the Soviets.

He thanked the assembled local business executives for coming and told them how much he wanted to stay in Congress. Retirement, he said, had given him an ulcer.