Some of the scenes look as though they belong on "Sesame Street," with one featuring a 5-year-old playing with toy building blocks, the other offering an animated version of a child's crayon drawing of stick figures, a house and the sun.

Two others look like slick political campaign spots, one featuring President Reagan boarding Air Force One and a triumphal ticker-tape parade, the other offering a Joe Sixpack working-stiff type earnestly pleading with his president.

But it's not a political campaign or children's advertising, it's "ad wars," an unusual confluence of 30-second television commercials focused on the U.S.-Soviet summit in Geneva and one of its major issues, the highly controversial, proposed nuclear missile defense system popularly known as "Star Wars."

The cartoon-like spots are being fired back and forth in an advertising war between both proponents and opponents of the "Star Wars" proposal, formally known as the Strategic Defense Initiative (SDI).

The campaign-type spots, sponsored by the Union of Concerned Scientists, are aimed at Reagan and those who influence him, in the hopes of putting pressure on him to reach a substantive arms control agreement with the Soviets. They evoke high expectations for Geneva by portraying the meetings as historic sessions that have the possibility of producing agreements that could protect generations from nuclear war.

Overlying the "Star Wars" fight is a suit by movie producer George Lucas, creator of the "Star Wars" movie trilogy, protesting that the ad-makers are violating his trademark rights. Lucas failed to get a temporary restraining order this week blocking the use of the "Star Wars" name in the ads.

Futhermore, Daniel O. Graham, a retired Army lieutenant general and a leading advocate of the defensive system, said his ad campaign would be over before further hearings are held on Nov. 25, because they are aimed at next week's summit conference.

So are the Union of Concerned Scientists' ads. One, entitled "Godspeed," has been shown during the morning and evening news shows on channels 5, 7 and 9 in the Washington area this week and several times on Cable News Network last Friday, the eve of Reagan's departure for Geneva.

Narrated in the majestic tones of actor James Earl Jones, it opens with shots of craggy, snow-covered mountain peaks.

"The Geneva Summit," Jones intones. "They meet at last. Two men. One question. Will there be an end to the nuclear arms race or do we race on . . . to the end?" The ad switches to film of Reagan boarding Air Force One. "You carry our trust to Geneva, Mr. President. We wait, we hope. History holds its breath."

The scene changes to a ticker-tape parade with a band marching down a street.

"Return with success. Bring us a future and we will celebrate your triumph for a hundred generations."

The commercial ends with a shot of Air Force One flying off on the other side of the confetti blizzard. "Godspeed, Ronald Reagan."

The second ad shows an actor portraying a working man:

"Mr. President, respectfully, I don't know much about bombs or 'Star Wars.' I'm just a working man with a bad haircut. But . . . . maybe the best thing you can do on Nov. 19 is drop a bomb on the Russians. A verbal bomb. A real proposal to end the arms race. This summit is a chance to do something bold . . . . To waste it would be almost as tragic as dropping the bomb itself. So for God's sake, sir, please don't blow it."

The crayon drawing ad is the centerpiece for the $1.7 million campaign by High Frontiers, the lobbying group for "Star Wars." The theme of the campaign is, "You are not now defended, but you can be."

The little girl narrating it says that her daddy told her that "right now we can't protect ourselves from nuclear weapons and that's why the president wants to build a peace shield. It would stop missiles in outer space so they couldn't hit our house."

A blue crayon arc is drawn over the house, the stick figures and an apprehensive-looking sun that then smiles. Red bombs pop like burst balloons when they hit the shield line.

"Then nobody could win a war. And if nobody could win a war, there's no reason to start one. My daddy's smart."

This ad prompted a reply by the Committee for a Strong, Peaceful America, a coalition of eight arms control groups. Running on local television stations this week, it shows a 5-year-old boy watching the crayola ad and playing with toy blocks that spell out "Star Wars and "Peace Shield."

"Matthew has the same problem the White House does," says the narrator. "He's trying to turn 'Star Wars' into . . . the 'Peace Shield.' . . . . When someone wants to mislead you, they try to change the name, but it's still the same old thing."

Matthew puts the blocks together to spell a third phrase and exclaims, "I got it: Space Wars."