Nancy Reagan yesterday named Jack L. Courtemanche, 50, chief of her East Wing staff, her fifth chief in that many years but her first to be a Ronald Reagan "loyalist" whose ties predate his 1976 presidential campaign. He will begin work March 10.

*Courtemanche, now executive director of the White House Conference on Small Business, will succeed Lee L. Verstandig, 48, who announced 24 days into the job that he was resigning to return to the private sector. Verstandig will be working on strategic planning in the consulting firm of Michael K. Deaver, the longtime Reagan aide and confidant who had recommended him for the East Wing job.

Deaver also was involved in hiring Courtemanche. Once the East Wing possibility came up, things happened quickly, Courtemanche said yesterday. "I started discussing it on Monday with Mike Deaver," he said. He met with Mrs. Reagan anc accepted the job on Wednesday.

Yesterday's White House announcement said that Courtemanche will be a deputy assistant to the President, the same rank held by James S. Rosebush, East Wing chief for four years until he left the White House in January. Verstandig had come into the position one rank higher, as a $78,000-a-year assistant to the President. Courtemanche said his salary will be $73,600, the same as his current one.

Courtemanche, who describes himself as "very cost conscious," said it does not bother him that the position has been returned to the deputy rank. "Oh, no, not at all," he said. "I was a deputy assistant to the President before at the White House. I feel very comfortable in that position, and that's where I think it belongs."

He said he does not yet have a comprehensive idea of what the first lady's chief of staff does because he has had "very little chance" to talk to Verstandig. That should change starting today, however. Courtemanche said both he and Verstandig will be among the staff leaving today on the White House preadvance trip to the Far East to prepare for the May Economic Summit.

Other than press secretary Elaine Crispen, whom he has known since both were early Reagan volunteers, Courtemanche said he does not know the East Wing staff though "they seem to have been doing a good job."

"Everything seems to have been running smoothly," he said, continuing that, "I've bought a lot of businesses in my lifetime, and have run a lot of companies and run different government operations. And I'm not one to make a lot of changes. I really like to work with the people who are there."

He said he believes that his strength is "working with people, being very willing to do all the tasks they might do. I really believe in teamwork."

Sources say that Verstandig, formerly undersecretary of Housing and Urban Development, ran into trouble with Mrs. Reagan and her 15-member East Wing staff when he brought along his HUD deputy, Theresa Elmore Behrendt, intending to install her in a similar job in the East Wing.

On Thursday, Behrendt, who earns $66,232 at HUD, reportedly was ordered back to HUD where she was given a new title of "acting special assistant to the Secretary," working on special projects.

Courtemanche said yesterday he has "no plans at all" to appoint a deputy.

"He's got a very secure ego, a successful person who doesn't need to be pushing himself out in front," said Jim Lake, who with Lyn Nofziger and John Sears first hired Courtemanche in 1975 for the grass-roots Reagan committee prior to the 1976 campaign.

"Jack is a patient and long suffering person who can deal with the strong personalities of the White House staff, a lot of people who have a wide variety of ideas about how to utilize Mrs. Reagan in support of the president," Lake said.

Nofziger said he remembers when Courtemanche walked in, having been referred by Deaver, and said he wanted to help. "We put him to raising money. He worked hard. He's been with us ever since."

*Between 1976 and 1980, Courtemanche was treasurer of Reagan's political action committee. In 1980 he headed the campaign in California. He did not come to Washington until 1983, after he sold his transportation manufacturing company, Crown Coach Corp. For eight months, he was executive director of the White House Conference on Productivity. In October 1983, Reagan named him deputy assistant for public liaison, then nominated him in February 1984 to be administrator of the General Services Administration.

The nomination got stalled in the Senate when questions about his business practices were raised because of litigation over the sale of Crown Coach. Courtemanche had sued for a final payment, and the buyers had countersued, challenging the firm's auditing practices. In early 1985, the suits were settled and dismissed with prejudice. Under the terms, the buyers were to make payment. Meanwhile, the nomination had lapsed when Congress adjourned for the elections, and Reagan did not resubmit it.

Losing out on the GSA job was a disappointment, Courtemanche said yesterday. "But that's what happens on the turf back here."

After the elections, still as a deputy assistant, Courtemanche did special projects for Deaver and then-White House chief of staff James Baker. Last April Reagan named him head of the 1986 White House Conference on Small Business.

Courtemanche and his wife Jo, who live in Georgetown, have six children, aged 18 to 26.