Politicians who worry about facing their constituencies after they have been voted pay raises probably should take lessons from Vincent Sombrotto, president of the National Association of Letter Carriers.

At the union's national convention in St. Paul, Minn., last week, the popular Sombrotto got a $28,512 raise (the typical letter carrier earns about $25,000 a year) and was reelected by acclamation, even though the union's official election is more than a month away.

The pay increase, the first for a letter carriers association president since 1978, gave Sombrotto the same percentage raises that rank-and-file workers have won in union contracts during the past eight years. It brings his annual salary to $93,650.

Because there was no announced opposition, Sombrotto was reelected on the spot, along with four of his five top officers. Other national and regional officers, including longtime Executive Vice President Tony R. Huerta, must stand for reelection this fall when the union sends ballots by mail to its 200,000 members.

In the coming weeks, most of the postal and federal unions representing 60 percent of the civil service work force also will hold conventions and elect top officers.

Most of the officers are seeking reelection, and, in some cases, healthy raises. Few of the union chiefs, however, will enjoy the luxury of a convention run as smoothly as that of the letter carriers.

They consider themselves the federal labor movement's shock troops, and have a history of directing their public hostility outward, usually at selected politicians and Postal Service managers.

Although the union has its share of internal blood-letting, its battles are usually fought before the conventions take place, making the gatherings appear more tranquil than those of many sister unions.

"In 50 years, the NALC has had only about five presidents," said the national officer of a rival union. "Members of Congress get the message that the NALC leadership has the troops behind it. That's why they have this image as the united shock troops."