Until recently, some supporters of Jesse L. Jackson had begun to grow weary of his many crusades.

After watching Jackson make two bids for president and seeing him dart around the world addressing issues as varied as toxic waste disposal, the Middle East and apartheid in South Africa, they wondered where it all would lead.

"I don't know how long this roving ambassador without a portfolio is going to last," Earl Shinhoster, Southeastern regional director of the NAACP said recently. "It may be time {for him} to grow some roots."

So, when Jackson announced Thursday that he will seek election this fall as a shadow senator to lobby for D.C. statehood, it was welcomed by some supporters as a move that could bring focus to Jackson's seemingly amorphous crusade.

Some national and local political operatives said that, despite obvious drawbacks, the shadow senator job could prove a useful vehicle for Jackson to lay groundwork for a third presidential campaign in 1992.

Or, if the seemingly impossible happens and Jackson somehow manages to win enactment of D.C. statehood legislation, he would be all but assured of election to the U.S. Senate.

"It does give Jesse a very highly visible political platform from which to continue his agenda," said Georgia state Rep. Tyrone Brooks, a Democrat who served as Georgia state coordinator for Jackson's 1984 presidential campaign.

Jackson made it clear, in announcing his candidacy at Howard University's Blackburn Center, that he intends to use the office as a pulpit in his ongoing campaign for black political empowerment.

He told the gathering of more than 100 people that achieving statehood for the predominantly black District "may be the only way to integrate the U.S. Senate," and he pledged to promote statehood nationally as "the most important civil rights and social justice issue in America today."

Jackson also said he intends to press the Democratic Party, which has included support for D.C. statehood in its platform, to fully back the effort to make the District the 51st state.

The D.C. Council in March approved the election of two unofficial senators and a representative to lobby Congress for statehood. With virtually no opposition, Jackson is expected to sail to victory in the Sept. 11 Democratic primary and the November general election.

Businessman John Hechinger Sr., who decided against running for one of the seats, said the council's failure to provide funding, authority and clear direction for the shadow offices raises questions about the seriousness of the posts.

Moreover, Jackson, in taking leadership of a statehood campaign that has suffered years of setbacks, may be faced with unrealistic expectations of what can be accomplished in the next several years. President Bush has said he would veto D.C. statehood legislation on constitutional grounds, and congressional Republicans are opposed to it because it would virtually guarantee the election of two more Democrats to the Senate.

"Jackson has got to do some miracle work to make this a plus for his political ambitions," Hechinger said.

Others, however, contend that the vagueness of the job might benefit Jackson, who could mold the office to fit his political needs while traveling the country in the name of statehood. Although the shadow seats will have no official standing in Congress, Jackson has indicated that he would make the most of the title.

Howard University political science professor Ronald Walters, a Jackson confidant, said the civil rights veteran would have a "quasi-official role" that "is not something that would take all of his time."

"I think it is ideal for Jesse," said D.C. school board member R. Calvin Lockridge (Ward 8), one of several board members who clashed with Jackson after Jackson moved his political operation from Chicago to the District last year.

"I think he will attempt to use it as a political platform," Lockridge said. "He'll fly out to meet with the right people in all of the right states. That will give him visibility."

Several local and national black leaders said they believe Democratic Party leaders will try to barter support for Jackson's statehood campaign in exchange for his pledge to stay clear of the 1992 presidential campaign. Jackson said he has not ruled out a run for president in 1992.

Brooks suggested that the lobbying post may be Jackson's last chance before the 1992 presidential primary to address the often-repeated criticism that, beyond his civil rights credentials, Jackson is a politician without a political re'sume'.

That criticism has hounded Jackson since his first bid for president in 1984. Jackson has been rumored as a possible candidate for several other posts, including mayor of Chicago, U.S. senator from South Carolina and D.C. mayor. In February, Jackson announced that he would not run for mayor in the District -- a decision that drew sharp criticism from those who thought Jackson had passed up an important opportunity to demonstrate his political skills and to help the District during a difficult period.

Jackson, asked in an interview last week whether he was running for the shadow senator's seat to add to his political re'sume', said: "My re'sume' on leadership and service is not something that is lacking. Can {Vice President} Quayle match my record of service. Or Bush?

"What I do is not driven by critics," he said.

Brooks, a veteran civil rights activist, said that in recent years even some of Jackson's staunchest supporters have become concerned that he is more interested in mounting "symbolic" campaigns than winning elections.

"A lot of us in 1988 did not support him {for president} because we felt that 1984 was enough. I told him that I didn't have the time to play around with another presidential campaign," said Brooks, who quit as Georgia coordinator of Jackson's National Rainbow Coalition in 1987.

"In terms of getting down in the trenches and doing the serious work, I think the perception is that Jesse isn't ready to roll up his sleeves and do that."