Midway through their 60-day coast-to-coast blitz to promote fundamental revisions in Social Security, President Bush and others in his administration have been unable to pry loose any Democratic senators from the solid wall of opposition.

As a consequence, Republican lawmakers are beginning to doubt whether the president can succeed in establishing individual investment accounts under Social Security.

After appearing with the president on Wednesday at a Social Security rally in Iowa, Senator Charles E. Grassley, Republican of that state and chairman of the Finance Committee, said, "There is not the significant momentum it takes to get a bill through the Senate."

In a separate interview, Mr. Grassley, who supports individual accounts and whose position makes him the most important senator on the issue, said he planned to put Social Security legislation before his committee in July but added, "The president may not succeed in as clear-cut a manner as I might have hoped."

Some Republicans who met with constituents on Social Security during the two-week Congressional recess, which ends Monday, reported that the president and his allies had managed to convince many people that the solvency of Social Security was in jeopardy and that the program needed to be overhauled.

But many Republicans said their constituents were wary about individual accounts as the best solution.

"Having just held 15 town meetings in my state," said Representative Jim Leach of Iowa, whose district includes Cedar Rapids, where the president spoke, "I think it is clear that the solvency concern is taking root. It is also clear that support of personal accounts has maybe slightly increased, but opposition has hardened substantially."

Mr. Leach, who flew back to Washington with Mr. Bush on Air Force One and who said he was "open to the possibility of personal accounts," questioned whether the president could overcome the united front presented by the Democrats.

Democrats, Mr. Leach said, "look at this as their chance to take control of Congress."

Whatever the reason, people who have worked on Capitol Hill for generations said they could not remember a time when Democrats in the Senate were so unified. 

Except for Senator Ben Nelson of Nebraska, who says he has not made up his mind, every Democratic senator is committed to opposing diverting Social Security taxes into individual accounts.

"We have continued to stay together," said Senator Harry Reid of Nevada, the Democratic leader, "because the president's plan is so flawed."

Under Senate rules, no legislation can be brought to a vote without approval of 60 senators. There are 55 Republicans in the Senate. So even if all of them backed Mr. Bush's plan, he would still need five more votes.

In the House, where passage of legislation requires only a simple majority, Republican leaders could probably win passage of a Social Security bill by invoking party discipline. 

But these leaders say they want the Senate to vote first on the issue to avoid a difficult and unnecessary vote in the House if Senate approval is not possible - to avoid, in other words, what is known in Congressional cloakrooms as being B.T.U.'d. 

The term refers the situation in 1993 when House Democratic leaders used all their might to persuade wavering Democrats to vote for President Bill Clinton's unpopular plan to place a tax on energy based on the number of British thermal units produced. The plan barely passed in the House but was then immediately shelved by the Senate and never considered again. Republicans won control of the House in the next election, and many Democrats attributed their defeat to their ultimately unnecessary vote on the energy measure.

In an interview published this week in National Journal, House Speaker J. Dennis Hastert said that even if Social Security legislation could pass through the Senate and House this year, there might not be time to negotiate a final bill until next year. 

Administration officials say they are undaunted and still expect to win the fight. "We're at the halfway mark of our 60-day tour and well beyond our events goal already," Treasury Secretary John W. Snow said on Friday. "The national dialogue that the president called for in the State of the Union is well under way, and Social Security has been elevated to the top of the national political debate. We're making real progress."

On March 2, Mr. Snow began a campaign he called 60 Stops in 60 Days to promote the president's Social Security goals. Since then, the Treasury Department said, administration officials have participated in 108 events in 32 states, including more than 40 town meetings with senators and representatives. 
Mr. Bush had 12 Social Security rallies in March, Vice President Dick Cheney 4 and Mr. Snow 10. 

The Republican National Committee calculated that Republican House members held more than 500 town meetings over the recess in which Social Security was discussed, and several Republican senators had similar events.
The two sides in the debate stepped up their television advertising over the Congressional recess. 

Supporters of the president ran advertisements comparing the Social Security system to the Titanic and others showing a ticking stopwatch counting down the time until Social Security goes broke. 

But there is a split among Republicans. The Club for Growth, which raised more than $20 million last year to support Republican candidates, is running a commercial criticizing Senator Lindsey Graham, Republican of South Carolina, because he has proposed legislation for individual accounts under Social Security that would include a tax increase.

AARP has advertisements on cable channels and in more than 200 markets comparing the administration's Social Security restructuring to the flattening of a house because the kitchen sink is clogged.

A group of veteran Democratic operatives including Jim Jordan, Senator John Kerry's first campaign manager in last year's presidential race, and Harold Ickes, President Clinton's political adviser, plan to begin television commercials next week against the president's plan.