Every Friday afternoon all year, Rep. Edward W. Pattison (D-N.Y.) dashed to National Airport to catch the 4:28 flight to Troy for a weekend of campaigning.

Every Hill recess, he was there to greet the early morning shift at factory gates, attended coffees, speak to high school groups, lunch with service clubs and talk with voters wherever he could find them.

And all year long he and his staff helped constituents and kept them aware of it with new methods such as mobile offices, town meetings, hot lines to Washington and other means of communication that the new breed of legislators has developed to a fine art.

It is for good reason that Ned Pattison is constantly running. He is the only Democrat in this century to go to Congress from the 200-mile-long district stretching along the eastern edge of New York from Lake George south to the Catskills.

Pattison is a member of the remarkable Class of '74, the Watergate Babies. The 75 Democrats elected to the House for the first time that year after Richard M. Nixon resigned the presidency picked up 49 Republican seats, many in areas thought hopelessly out of reach for a Democrat.

Because of their numbers and the supposedly fragile political position of most, they banded together when they came to Washington and pooled ideas on how to get reelected. They worked hard at it and with extraordinary success.

Usually after a landslide such as Democrats enjoyed in 1958 and 1964 the pendulum swings back two years later and the other party recovers many of its traditional seats. That didn't happen two years ago.

In 1976 all but two of the first-term Democrats who sought reelection won. And one of the two probably would have won if he hadn't tried to solicit sex from an undercover policewoman.

What made the difference and brought most of them back for a second term was their effective constituent service. Once a member of Congress has established personal trust, voters may forgive some votes they don't like.

The Class of '74 may not fare as well this year as it did in 1976.

Several were reelected two years ago by a handful of votes. The weather this election day could make a difference. Other factors, such as the absence or the presence of third-party candidates could turn a district around. Some Republican House candidates may have lost last time because they were stripped of money and other resources by a party concentrating on the presidential race.

Sixty-eight of the 75 Democrats elected four years ago are running again. Two-thirds are considered shooins or reasonably safe bets for another term. But 10 to 20 of the seats may be up for grabs.

A recent survey by Congressional Quarterly turned up Ned Pattison, 46, as the most vulnerable of this group.

The fifth generation of his family to practice law in Troy, where the Mohawk and Hudson rivers converge, Pattison worked as a young Democrat for John F. Kennedy in 1960, won 43 percent of the vote in his first try for a House seat in 1970, then settled for being elected county treasurer.

In 1972 the incumbent Republican won 70 percent of the vote. But two years later came Watergate. Rep. Carleton J. King was old and sick. Pattison won with 53 percent of the vote.

Pattison was a founder of the 94th Caucus (Democrats first elected in 1974) and has served as chairman. This has proved a cohesive mechanism, begun to muster strength for procedural change in the House, and continued to discuss legislation and share ideas on how members could get reelected. "That's how we all survived," says PattisoN.

Like most of his class, Pattison has been somewhat more liberal and a more consistent supporter of President Carter than the average House Democrat. He also typifies the Class of '74 in bringing to Congress mythshattering ideas that you don't have to go along to get along and that the pork barrel and defense budget are not sacrosanct. He voted against the B1 bomber and supported the Panama Canal treaties.

Two years ago, with a third candidate in the race, Pattison won a second term by 4,187 votes and 47 percent of the total vote. The third candidate was a conservative, but so far conservative, Pattison says, that his simplistic proposals probably attracted some low-income voters who normally would hvae voted Democratic.

Supporters say Pattison won and will win again because he comes across as open and honest. Perhaps too open.

A recent poll that became an article of Congress whether they had used in Playboy magazine asked members drugs. Pattison replied that he had tried marijuana while vacationing out of the country. As it happened, he was the only responding congressman to permit use of his name. His conservative opponent, Jerry Solomon, has found occasion to mention it.

Pattison talked about all this last week on the afternoon flight home after being called to Washington as part of a small group of members of Congress to meet with President Carter to discuss the anti-inflation program Carter was to unveil that evening.

"Yeah, I think so. People vote for you because they think you worked hard, you communicated with them, they trust you," he said.

Until a month ago, even Pattison's campaign staffers figured he was a loser this year. The building trades unions were mad at him because he voted against the common-site picketing bill. Solomon was campaigning full time, while Pattison had to spend most of his time in Washington.

Now, Pattison's staff thinks he has turned it around, besting Solomon in debates and getting a big lift from an appearance by Vice President Mondale. Pattison requested Mondale rather than Carter because the vice president's travel expenses cost the candidate only half of what Carter's would.

An Albany reporter who has followed the Pattison-Solomon race thinks it is too close to call. If Pattison makes it back to Congress, it will be because of good constituent service, she said. "People say, 'I don't agree with him, but I trust him,'" she says.

Across the state line in northwestern Connecticut, Pattison's Democratic classmate. Toby Moffett, appears to be cruising to a third term. Moffett, 34, was one of the most visible of the antiestablishment boat-rockers when the Class of '74 came to town and later led the fight against deregulation of natural gas. Moffett's face peers out from billboards with his name. "Toby," and the message "People before politics."

According to special reports to the Washington Post, some other close races involving Democratic members of the Class of '74 include:

In eastern Long Island, Jerome A. Ambro always has tough going because of the strong Republican organization in Nassau County. But the Republican candidate this year suffers from a shortage of money, which is being concentrated on the gubernatorial race.

Robert W. Edgar, a former college champlain, has never got a firm grip on his district in the suburbs south of Philadelphia. Edger has not tempered his liberal views to fit the more conservative area. Loss of defense contracts has been blamed on his anti-Pentagon votes. He is expectd to win narrowly.

In Michigan, M. Robert Carr was twize elected to his lansing seat by narrow margins. He is more liberal than his district but has won on constituent service, and probably will again.

In Illinois, Abner J. Mikva, a liberal leader of the House who was in and out and back again since 1974, faces another tough race on chicago'y affluent North Shore.

In Topeka, Kan., Martha F. Keys weathered a divorce and remarriage to Rep. Andrew Jacobs Jr. (D-Ind) to win with less than 51 percent in 1976, and having done so her vigorous campaign astyle is exected to reelect her.

West of Denver there is a rerun between Timothy E. Wirth, who won two years ago with 50.5 percent of the vote, and Republican state Sen. Ed Scott, a former television kiddle-show host. It is a classic liberal-conservative race in the diverse district. The general impression is that Wirth has grown in the last two years and Scott has focussed his campaign too narrowly.

In the Los Angeles suburbs, Mark W. Hannaford, who squeaked by with a margin of 2,800 votes, is in a rematch. Both sides say they are better organzied this time. Hannaford opposed California's tax-cutting Proposition 13, voted last June.