NEW YORK, March 3 (Reuters) - U.S. states need to "rally together" to maintain safety measures like social distancing and mask-wearing while the federal government helps ramp up production and delivery of vaccines, the White House said on Wednesday.

Cases of COVID-19 in the United States remain upwards of 50,000 daily even after the U.S. government has distributed more than 100 million vaccine doses and put shots into over 50 million arms, according to federal data.

"This is not forever ... we know that it can save tens of thousands of lives," White House senior adviser Andy Slavitt said on a Wednesday press call of continuing safety measures after Texas and other states said they were rolling back some pandemic-related restrictions.

"We strongly encourage people to continue to wear masks, and mayors, governors and others - recognizing that they have difficult decisions to make - to keep the course."

Slavitt said the federal government is planning to spend $100 million to help the joint partnership between Merck & Co and rival Johnson & Johnson announced on Tuesday accelerate vaccine production.

The infusion will help J&J ramp up production of its one-shot vaccine, Slavitt said.

J&J was contracted to deliver 200 million doses to the federal government by the end of May and roughly a billion doses globally by end-2021.

"Over time we believe Merck will be able to double the capacity of Johnson & Johnson," Slavitt said.

U.S. President Joe Biden said on Tuesday the United States will have enough vaccine supply to inoculate all adults by May.

J&J, Pfizer Inc, and Moderna Inc are contracted to deliver 700 million doses by mid-year between them.

Slavitt urged states like Texas to reconsider recent decisions to lift mask mandates and allow businesses to fully open without restrictions.

There are health officials in every state who feel "now is the wrong time to lift the mask mandate," he said.

(Reporting By Jarrett Renshaw and Carl O'Donnell; Editing by Sonya Hepinstall and Bill Berkrot)