The change in policy by Domino's could have a profound impact on the way the company does business, and ultimately on its sales. Unlike Pizza Hut, a subsidiary of Pepsico Inc. that operates 4,443 carry-out units among its 7,800 United States restaurants, Domino's depends largely on delivery services. The company said it expected to report about $2.3 billion in sales this year. Rivals Could Benefit

While it periodically altered or expanded its menu, Domino's biggest selling point was speed of delivery, aided in recent years by computer listings of customers by phone numbers, to track their names, addresses and preferences for regular pizza or thin-crusted, green olives or black, diet cola or regular.

The difference between ringing the doorbell within 30 minutes instead of, perhaps, within 35 may sound small. Marketing experts contend, however, that canceling the guarantee may send consumers to other pizza delivery companies, like Little Caesars, or to neighborhood Chinese restaurants.

"It's one of those things that is difficult to define," George Thompson, a restaurant chain analyst with Prudential Securities, said of the potential impact on Domino's sales. "But the point is, it's not great. With a major competitor like Pizza Hut, where the quality is very good, service becomes an important factor. With Domino's, the fact they built their business by delivering in a timely fashion is also important. Now they will not be able to deliver so timely.

"In general," Mr. Thompson added, "that could be a negative perception."

A negative perception might also be building as a result of the lawsuits against Domino's for accidents involving delivery people, all of whom use their personal means of conveyance for the job. Suits and Settlements

In May, the company agreed to a settlement of $2.8 million with the family of Susan Wauchop, a 41-year-old woman from Calumet City, Ill., who was struck and killed in her van three years earlier by a Domino's delivery driver. The plaintiffs charged that the driver was negligent in trying to arrive within the promised time.

In August, Matthew D. Jacks, a 19-year-old man from Lewiston, Me., sued Domino's, contending he was struck by a driver in March, causing injuries to his pelvis, knee and thumb.