Ed Scott and Jerome Williams were sitting in the living room of a modest middle-class row house here Thursday night, watching television.

If that doesn't sound very exciting, well, they weren't finding it particularly riveting themselves. But it's still worth looking in on them, because it's on such semi-dull Thursday nights that presidential elections are won and lost.

Scott and Williams are black Philadelphians, and as such their reaction to the show they were watching -- the Democratic National Convention -- is important.

In 1976, Jimmy Carter got nearly 200,000 black votes in Philadelphia -- 90 percent of an unusually large turnout. Those votes were crucial to his carrying the city by more than 250,000 votes. And that Philadelphia margin was enough to overcome Gerald Ford's lead in the rest of the state.

This year, Pennsylvania and its 27 electoral votes could easily switch to Ronald Reagan. The state's governor and both its senators are Republicans. rGeorge Bush is popular here. Philadelphia gave its heart to Sen. Edward M. Kennedy this spring, rolling up huge majorities for him in the Pennsylvania primary. In 1976, Mayor Frank Rizzo strongly supported Carter in the fall campaign; in 1980 Mayor William Green has so far strongly supported Kennedy.

That doesn't mean Carter won't carry Philadelphia. This being a Democratic city, he almost surely will. The question is by how much. If Reagan lures away enough blue-collar whites, and if enough blacks stay home, then Carter's margin here won't be big enough to carry the state.

The convention was a chance for him to sell himself to a wary Philadelphia.

But Philadelphia, judging from an unscientific sampling, was underwhelmed.

Scott and Williams liked Vice President Mondale's speech, but when a film about Carter came on, they got bored.

"Well," said Scott, a lean, weary-looking man of 43 who is a metal inspector at the Philadelphia Navy Yard,"I guess I thought about Kennedy and I'll think about him in the next election." There was a tone of slight disappointment in his voice. "The only thing that makes me stick for Carter is that inside he has good that wants to come out."

"That's right," said Williams, 32, a nattily dressed data processing specialist at a bank. "If Kennedy had been the nominee it would have put in Reagan. Sure, a lot of grass-roots blacks are for Kennedy. But the blacks that look at what Carter's done, they'll be for Carter."

Andrew Young, former ambassador to the United Nations, came on the television and said President Carter does what's right not what's popular.

"He damned sure does that," said Williams.

"A black man has got to be a fool to vote for Reagan," said Scott.

By this time the two men had worked themselves into a semblance of enthusiasm, but it was a little strained. Earlier in the evening, Williams had chaired a meeting of his neighborhood association and asked those in attendance who they supported for president. There were no hands for Reagan, a forest for Kennedy and one for Carter.

Then he invited everyone back to his house to watch the acceptance speeches. Only Scott came, and he left in the middle of Carter's speech. The Williams children sat outside on the porch and chatted with neighbors. His wife went upstairs to bed.

Just before Carter finished speaking, a neighbor dropped by to borrow $10. "Is the speech any good?" she asked Williams.

"Well," he said; "It's an honest speech. But it's not an emotional speech."

At least Williams watched. Donald Hall, 31, a social worker didn't.

"That convention doesn't mean nothing," he said. "It's just something on the tube. In '76 Carter came here and made big promises, and I worked in his campaign. I'm not this year. It's a fallacy to assume he has the blacks sewed up. It's not there anymore."

Earl Morgan, 31, a butcher, didn't watch, either. "If the president does not go with Ted Kennedy's plan that he put on the floor," he said, "the black vote will not go with him. If he doesn't do that, I can't see voting for him."

A world away in white, ethnic, working-class South Philadelphia, Joe Campagna, 49, a construction worker and president of the First Ward Italian-American Club, also had his television set tuned elswhere. "I'll be honest," he said over the noise of the Phillies' game on the club's television, "I don't like Carter. He hasn't showed me a damned thing. You know, years ago this used to be called the Italian-American Democratic Club. But I took the Democratic out when I took over. We're Republicans now."

The crowd at the Thirty-Fourth Ward Democratic headquarters, in an Italian pocket of predominately black West Philadelphia, watched a Cary Grant movie instead of the convention while they waited in line to ask small favors of their ward leader, state Rep. Nicholas Pucciarelli.

"I don't think there seems to be too much of an interest in the convention," Pucciarelli said. "They think it's kind of cut and dried. To be honest with you. I think we're gonna have a problem with Carter."

William Neill, a gruff, gray-haired, 66-year-old widower, retired construction worker and lifelong resident of South Philadelphia, was watching the convention, but not altogether enthuslastically.

When a lemonade commercial came on he leaned forward and said obstreperously, "Talking about Country Time lemonade why, it doesn't even have any lemons in it. I read it in a magazine."

Then the commercial ended and the ABC's "20-20" show came on with a story about the singer Billy Joel. That played better with William Neill. s"I like this channel," he said. "They got that guy with the gray hair on, what's his name? Frank Reynolds. Plus, when the convention gets boring they cut if off a lot to this "20-20"."

Neill started watching the convention with his mind made up: He had voted for Carter in 1976, but he wouldn't vote for him again. He was too angry about inflation and about the hostages in Iran.

But as the convention wore on, his resistance was weakening. He thought Kennedy have "a hell of a speech." He decided Carter was, if nothing else, sincere. When the camera showed Rosalynn Carter, he said, with grudging affection, "Aw, I like her to a point. I think she tells him what to do. But she's got a lot of personality."

"I was going to vote for Reagan," he said, "but now I'm on a cliff. I don't know. I started voting for Roosevelt in the '30s. I liked JFK. I found Teddy's speech interesting. I think I'll watch and see if Kennedy pats Carter on the back."

He smiled mischievously. "And if he does, I won't vote for either one." Score one for the Democrats.