Dave D'Addio walked to his mailbox one day recently and found a plain brown envelope. Inside was the preseason all-Italian-American football team, and D'Addio was listed at the first running back.

"I got a big chuckle out of it," D'Addio, the starting Maryland fullback, said yesterday. "I'm real proud of it because it's probably the only preseason all-anything team that I made."

If D'Addio (pronounced daddy-o) continues to play as he did Saturday in Maryland's 21-14 victory over Vanderbilt, there will be plenty of postseason honors that aren't so limited.

D'Addio caught eight passes for 113 yards and hurled his 233-pound body high over a pileup for a touchdown on fourth and one. He fumbled away a near-touchdown earlier, but still was the heart of Maryland's offense.

D'Addio's toughness is becoming legend in College Park. Bobby DePaul, a linebacker, went head to head with D'Addio during spring practice. DePaul is thinking of getting a T-shirt that reads, "I went six weeks with Dave D'Addio and I survived."

Said DePaul, "I'm glad he's a senior because I don't want to have to go through another spring against him."

Most stories about D'Addio concern his blocking. At 6 feet 2, and 228 to 240 pounds, he runs the 40 in 4.7 seconds, a combination of size and speed that can be very threatening when he is coming at you full speed. "He's a 240-pound shot of thunder," says quarterback Boomer Esiason.

"It's like having another lineman out there blocking for me," said tailback Willie Joyner. "I never see what he does technically; all I know is his man is never the one that tackles me."

D'Addio likes blocking almost as much as running or receiving. His teammates were still marveling yesterday at two "rhino blocks" D'Addio inflicted on Vanderbilt linebackers; a rhino block is when the defender is hit so hard the back of his helmet hits the ground.

"Dave is just a tough New Jersey kid," said Frank Costello, the Maryland strength coach, who graduated from Union High School a few years before D'Addio. (D'Addio adopted No. 44 from his high school idol, Larry Kubin--a Union graduate and Redskins linebacker--not his current idol, John Riggins.)

Costello has also monitored D'Addio's increase in strength over the past year. D'Addio returned to school weighing 241 pounds (10 heavier than last year) while having increased his vertical leap three inches to 31. The coaches stopped him at 400 pounds in the bench press.

D'Addio has dropped some weight but increased his durability. He played in 61 of 71 plays Saturday, even though it was 120 degrees on the turf. He even showed some new moves--the leap into the end zone and the ability to step around, not through a defender.

"When I went up for the touchdown, I didn't think I could get that high," he said yesterday. "I usually go through. I've been practicing a couple of moves, but my favorite move is still up the middle."

It's a wonder D'Addio chose to attend Maryland. He was recruited by Nebraska, Ohio State and Tennessee, among others, but those schools wanted him to be a linebacker or a tight end.

"Maryland was the only school that said I could would get a shot at fullback," D'Addio said.

He played linebacker for Jerry Claiborne in 1980 out of necessity, but missed the 1981 season with a knee injury and the first two games of 1982 with a groin injury that would have kept most players out another month. He averaged 4.5 yards per carry in nine games last season. But Saturday was the first time D'Addio played the season opener on offense.

Several NFL scouts have talked with Maryland coaches about the possibility of D'Addio's playing tight end as a professional.

"Nah, the guy isn't a tight end," Esiason said. "He's a fullback in the same mold as that other guy who wears No. 44--you know, the guy who plays for the Redskins."

Maryland announced yesterday that Saturday's 8 p.m. game with West Virginia at Byrd Stadium has sold out of its 50,000 seats.