LOS ANGELES, JAN. 2 -- Gov.-elect Pete Wilson (R) today named political ally and friend John Seymour, a relatively obscure state senator from Orange County, to replace him in the U.S. Senate.

Wilson described Seymour, a Republican, as "a compassionate conservative," adding, "I have known him well for a long time. . . . I have watched him carefully."

Seymour, 53, a former Marine and ex-mayor of Anaheim, has served in the state Senate since 1982. He is an entrepreneur who made a fortune in real estate development and was president of the California State Real Estate Association before entering partisan politics.

"I saw him bring to the administration of his city government the same keen intelligence, the same energy and toughness of mind that had made him a millionaire in business before he was 30 years old," Wilson told a news conference in Sacramento.

"The task ahead will not be easy because I must now demonstrate to the people of California, in a very short time period, that I am worthy of their trust and faith, and I intend to do exactly that," Seymour said. "I and my family are committed 110 percent to serve all of the citizens of this state."

The appointment, which becomes effective when Wilson is sworn in as governor Monday, came as a surprise. Sources close to Wilson said he was influenced by his liking for Seymour, who served as his campaign chairman when Wilson was reelected to the Senate in 1988.

These sources said two other factors played an important role in Seymour's selection. One is that he is a fellow former mayor, a mark in his favor with Wilson, who served as mayor of San Diego.

The other and possibly deciding factor is that Seymour has the financial resources and desire to run again in 1992 and 1994. The Senate term that Wilson is vacating will not expire until 1994, but California law will require Seymour to run for the vacancy to which he is being appointed at the next general election.

"When I was asked during the race for governor whom I would appoint as my successor in the U.S. Senate, I answered that I would appoint someone who was philosophically compatible with my own positions and someone who could be elected not once, but twice, over the next four years," said Wilson.

For the first time in its history, California will elect two senators in 1992, when Sen. Alan Cranston (D) has said he will retire.

Seymour faces formidable obstacles if he hopes to be more than a two-year senator, Republican officials said. He is virtually unknown in a state of nearly 30 million people where name recognition is a key to election. And while Seymour is fiscally conservative, his appointment is likely to be received with a lack of enthusiasm from social conservatives because he, like Wilson, supports abortion rights. He was defeated by an antiabortion conservative in his only statewide race, when he ran for lieutenant governor last year.

A veteran lobbyist in Sacramento who asked not to be identified said, "The Democrats must be rubbing their hands with glee at this appointment. Seymour is a complete unknown."

But none of the various Republicans who had been mentioned as Wilson's likely successor are well-known to the public either.

"The bottom line is that the {Republican} bench isn't strong," said Stuart Spencer, a longtime adviser to Wilson. "Seymour is a proven fund-raiser and a quick study on issues. He also has youth and fire in his belly."

Seymour also has two years in which to become known to an electorate that has, before Wilson's reelection, turned out first-term U.S. senators in three consecutive elections.

At the news conference, Seymour cited education, the nation's infrastructure, the environment, and drugs and violence as his main concerns in keeping alive a dream, "a vision for the year 2000."

State Sen. David Roberti (D-Los Angeles), commenting on Seymour's selection, said, "He is capable and hard-working and has been involved in a number of important areas in the state of California. Certainly his work combating substance abuse has been of significant value."

Seymour served as chairman of the state Senate's Select Committee on Substance Abuse and supports combining tough penalties for drug sales with a comprehensive prevention and treatment plan.

In endorsing him for reelection in 1988, the Los Angeles Times said: "Seymour lobbies without letup against the roller-derby mentality in Sacramento, working issues on a bipartisan basis, focusing on solving problems. . . . His interests range from freeways to Medi-Cal reforms, and he has made his ideas work in both."

While serving as mayor in 1979, Seymour negotiated the move of the Los Angeles Rams football team to Anaheim.

State Sen. Alfred Alquist (D-San Jose) called him "the best appointment for the position. He's a good man, and he'll do a fine job."